So, depending on your definition, you may not be very much hindered by “pacifism” at all. As I discuss for a divine oracle with similar needs, buffing often is what a spellcaster should do; the “fighting aspects” of the game, as that questioner put it, are usually best left to other characters.
However, I have concerns about what “pacifism” really means to you. It seems to me that, in Pathfinder, you have two choices:
merely paying lip service to the idea, while still actively encouraging and enabling violence albeit without personally getting your hands dirty,
or else being a significantly disruptive presence at the table, causing significant problems for the other players (and their characters too, but the players are the important part), because you have moved too far away from the things Pathfinder was made to do.
I’ll start my answer off by discussing healing and buffing and charming, as you request, but the meat of my answer is going to be about pacifism and what that means. I do offer an idea for how one might be able to straddle the line between these two and have an effective and authentic pacifist Pathfinder character, but that will depend a great deal on the nature of your campaign.
On healing
Healing, for the most part, is an out-of-combat, as-needed activity. As much as possible, it is most efficient to heal using wands and scrolls, rather than spell slots. Use a wand of a low-level HP-healing spell (cure light wounds, unless you can stomach the [Evil] tag on infernal healing) to top off after battles, and use scrolls of status-effect-healing spells to remove those annoying persistent effects.
In combat, healing is generally emergency-only. The cleric’s ability to spontaneously commute spells to cure spells is more than sufficient to cover this. Even stabilize is often enough at low levels.
At high levels, the heal spell does change this somewhat; unlike every other healing spell in the game, heal is huge and effective even in the middle of combat.
On buffing
Buffing is hugely useful and powerful. In fact, buffing is so good and clerics are so good at it that, depending on your definition (see below), pacficism may be no hindrance at all. For the most part, buffing well is pretty much “be a cleric,” and going into detail on how is beyond the scope of a reasonable answer here. Reading a cleric handbook is your best bet here. The aforementioned Q&A about the buffing divine oracle is also worthwhile, I hope. Ultimately you just have to disregard the aspects that don’t apply to you.
On charming
Charms and compulsions are very effective against certain kinds of enemies, and useless against a lot of others. These are extremely campaign-dependent for how useful they are. In the right campaign, I’d recommend taking a domain that gives you more of them, since the cleric’s usual options (suggestion, command) are one-off effects and to focus on this you’d rather charm and dominate. But in many campaigns these are going to be useless.
Also, again, the definition of pacficism is a big deal here. See below
On pacifism
There are a lot of different ways you could define pacifism. In your question, it seems to be very personal, to the point that it seems almost pointless. “I won’t hurt you— but I will empower my friend here to hurt you really, really badly.” You seem to OK “offensive” buffs, that don’t protect anyone, they just make someone more able to hurt others. That’s an extremely narrow definition of pacifism that doesn’t seem, well, honest – more like you’re deluding yourself into thinking you’re better, more moral, than those who actually get their hands dirty.
A step below this is “I won’t help my friends hurt you, but I will make sure they suffer no injuries while they do so, that nothing you do can stop them from hurting you.” This would be focusing on just healing and defensive buffing – buffs that prevent injuries or status effects, rather than those that directly improve offensive capability. The problem is, this is ultimately not all that different to me, morally. You are actively enabling violence; avoiding personally striking a blow is really just semantics.
Below these is when you are actively trying to avoid violence itself. One way to do that is with mind-affecting magic, but I would argue that forcibly taking control of another person’s mind is a much greater assault than just stabbing them. That’s not pacifism, that’s domination.
But you could avoid that, too; try to genuinely convince people to avoid conflict. At most, a calm emotions spell to keep tempers from getting in the way (though in a lot of cases, both sides have a pretty good right to be angry). This is much more “real” pacifism, but now you run into a different problem: Pathfinder is a game centered around violence. It comes from Dungeons and Dragons, a game that has its roots in pure dungeon-delving and dragon-slaying, and those things are what the rules focus on. The overwhelming majority of the game, between its rules, its narrative, its tone, and its characters, is focused on that. The skills system is underdeveloped and largely uninteresting; the social skills are so poor that the overwhelming majority of groups ignore them entirely and just roleplay social interactions freeform, with ad hoc Bluff, Diplomacy, and/or Intimidate rolls thrown in occasionally.
And not only is Pathfinder bad at the sort of game where you are well and truly a pacifist, but everything about it is telling the other players that this is not the sort of game where pacifism is a thing. Violence is an effective, accepted, and often morally-sanctioned solution to problems in Pathfinder. People show up to a Pathfinder game with this as an expectation. Trying to turn this on its head, eliminate the majority of the game, and sideline the other players’ characters, who are focused on combat because, hey, they’re Pathfinder characters and that’s what Pathfinder’s largely about, is simply rude.
So I think you need to sit down and think what, exactly, you mean by “pacifism,” and you have to either accept that your character is really only paying lip service to the idea, or that this character is going to be disruptive and problematic, and that you need to talk through the issues with the rest of your group (not just the DM). It very well may be that Pathfinder is the wrong system for this character, and you need to either convince everyone to try a system better suited to it, or shelve the character for another game in another system.
All that said, I will acknowledge a way to straddle the line, so to speak. Your character could have heartfelt ideals about pacifism, try to encourage violence-only-as-a-last-resort, and have personal boundaries on what the character is personally willing to do, but believe in the mission enough to support your allies even as they engage in violence.
This is a difficult line to walk, I think; it would be all too easy to slip off one side or the other, becoming a pacifist in name only or else becoming an annoyance at the game table. The character absolutely needs a huge quest, something to justify their support of violent individuals as they engage in violence. This is a character that would be very difficult to justify joining an adventuring party, say in a sandbox game. But in a more directed, epic quest to save the world kind of game, a character can more reasonably and more authentically accept and even support violence while still personally promoting pacifism.
You can do that with a regular homonculus
The homonculus seems to be able to perform what you are looking for. As written:
A homunculus's creator determines its precise features; some are more refined looking, but most creators don't bother to improve the creature's appearance beyond the minimum necessary for functioning.
So you can make it look like a cute maid or butler if you want.
As written in the Monster Creation rules, a construct typically get 2+int skill points per level. As the homonculus has an int of 10 and not -, you get 2 skill points per hit dice (although the points for the two first HD seem to be distributed in Perception and Stealth), and you can build it with as many HD as you want by paying more materials (2000gp per HD beyond 2).
Example of builds:
Homonculus with 3 HD. cost: 3050gp. Looks like a cute butler with a fez. skills for 3rd HD: two ranks in Profession(shopkeeper), feat for 3rd HD: Talent(Profession(shopkeeper)) -> +6 total bonus for his Profession(shopkeeper) tests. Not that great but enough to take care of usual clients.
Homonculus with 5 HD. cost: 7050gp. Looks like a cute maid with a witch hat. skills: 5 ranks in Craft(Alchemy), 1 rank in whatever you want. feats: Talent(Craft(Alchemy)), Master Alchemist. -> +10 total bonus for his Craft(Alchemy) tests, which is enough to craft the basic stuff, and thanks to the Master Alchemist feat it can do that fast.
However please note that an homonculus doesn't qualify for item creation feats since it lacks a caster level for that. They can however qualify for Master Craftsman.
Best Answer
Im very familiar with Iron Gods, its one of the adventure paths that is a high priority on my list of campaigns to GM. As such, I identified the construct you mentioned right away (Gearsmen), and I will say some spoilers about their behavior that you might not want to know, so skip ahead if you don't want spoilers:
With that out of the way, the easiest way to handle high DR (or hardness, in this case) is to obtain ways to cause Energy Damage, easily available from spells, alchemical items, and certain class abilities. To list a few easy solutions (and please, this is not an exhaustive list, but merely examples):
Hardness on creatures work a little differently than on objects (as explained on this answer, which is talking about Iron Gods's robots, by the way), as energy damage is not halved against them, and any energy damage caused is then reduced by their hardness value. This means that you want to use whatever energy type they are vulnerable to, as others will get reduced by 5/10 points and not really be effective.
Robots specifically are also vulnerable to electricity, so try to find a way to obtain a reliable source of shocking grasps, or bottled lightning and you will be golden. Not only they will take increased damage, but their Hardness will not apply. Acid flasks and alchemical fire won't really be a good idea against robots, as they are not vulnerable to fire or acid damage.
Constructs, in general, usually have a low Dex score, and bad reflex saves. This also means they have a low Touch AC, being easy to land touch spells and abilities on them, including alchemical items like those I mentioned (ranged touch attacks for thrown alchemical weapons).
Another spoiler about treasures from the adventure:
Another way to try to handle them is to group up and abuse maneuvers. For instance, disarming them will prevent them from electrifying their weapons, drastically reducing their damage output. Dropping prone and/or grappling one of them would allow other party members to have an easier time trying to land their attacks.