[RPG] the fastest way to earn money without adventuring

Question: How many people can help one person make a craft armor/weaponry check?

That would depend on the item being crafted. Let's start by looking at the RAW for aiding skill checks.

Aid Another

You can help someone achieve success on a skill check by making the same kind of skill check in a cooperative effort. If you roll a 10 or higher on your check, the character you're helping gets a +2 bonus on his or her check. (You can't take 10 on a skill check to aid another.) In many cases, a character's help won't be beneficial, or only a limited number of characters can help at once.

This clearly states that more than one aid roll can be made at once. So you can have multiple helpers. But how many?

In cases where the skill restricts who can achieve certain results, such as trying to open a lock using Disable Device, you can't aid another to grant a bonus to a task that your character couldn't achieve alone. The GM might impose further restrictions to aiding another on a case-by-case basis as well.

While a number of folks focus on the "you can't aid another to grant a bonus" section, I don't. As I read that passage it simply states that the +2 aid bonus can only be granted by a person who is able to do the act in question alone. In other words your aids must be competent as crafters in their own right. What is important in this passage, imo, is that it states the GM is free to impose restrictions on aiding another "on a case-by-case basis". This is were the GM can put some logical brakes on the whole affair. You need to work out what is a reasonable number of aids and that would be judged on an item by item basis. As example, crafting a longsword, DC 15, is easier than chainmail, DC 16. Both are doable with only one rank in the appropriate craft skill. But one could say, logically, that the number of aids for a suit of chainmail could be much higher than for a longsword.

I could reasonably see a dozen aids working on patches of chainmail for the main person to assemble into the final product. That is a huge time saver. So, call it twelve aids, imo.

But for the longsword, I could see two aids hammering it at once while the main person holds it and controls where blows fall. I could see this expanded to two teams of two, the first team hammering at a slightly faster rate and rotating out to rest and allow the second team to hammer for a while, also at a faster rate. The resting then rotating would allow them to bang a sword out a bit faster. The same teams would do the same kind of thing on the forge bellows to stoke the fire. It could even be stretched as far as three teams. Beyond that I think the rule of diminishing returns would make it worthless, ie the extra rest time is not needed OR the even faster hammering makes even normal quality difficult to control. So, no more than six aid rolls here, imo.

All this is great but remember that each aid still has to pass a craft roll, DC 10, in order to give the +2 aid bonus. Having to make these rolls (no taking 10) would be motivation enough for some GM's I've known in the past to limit aids more severely than I have in the examples above. Some GM's may even make one roll to cover all the aids making it all or nothing.

So, no easy answer for how many can help. You have to think about the item they are making and how teams would or could affect constructing it. It will work better for some items and not at all for others.

The best resource available is the Complete Cost Reduction Handbook, which can get your crafting gp costs under 5% of the market price, and also covers how to reduce crafting times and XP costs. The best methods are Extraordinary Artisan and Bind Elemental from Eberron Campaign Setting (Exceptional and Legendary Artisan cover time and XP, respectively). Magical Artisan from Player’s Guide to Faerûn is also a great addition, assuming you can mix Eberron and Forgotten Realms material – it reduces all of the above, though less than the individual Eberron feats do. Several guilds from Dungeon Master’s Guide II also can help.

The fabricate spell can speed up mundane crafting immensely. A dedicated wright (Eberron Campaign Setting) doesn’t actually make things faster, but it can craft for you while you’re off adventuring; this is a highly-recommended use of your Craft Homunculus ability. Unseen crafter from Races of Eberron can provide a similar function.

Avoiding the need to find the materials for sale is possible with true creation, but that is quite high-level.

This is extremely powerful, and will break most games, particularly in a campaign where 3.5’s systemic imbalances are exacerbated by less-than-usual wealth. An artificer could easily dominate such a campaign as it is; really pushing for reductions will dramatically increase the likelihood that you’ll become literally one of the dominant forces in the campaign world, long before your non-magical teammates could manage any such thing.