Thou shalt not sacrifice caster levels.
As the golden rule of 3.5 multiclssing, it's hard to beat the above. It's quite possible to apply requirements gathering methods to 3.5 as well as 4e, and estimate approximate to-hit and damage at each level.
Plan out your character to 20.
To answer:
s there an effective way to identify class combinations which seem appealing up front, but which will fall behind as the characters level up (without actually taking the character through its paces in a game)?
is simple: plan out your character to level 20. Identify, at each level, what benefit the character is deriving from your choices. Test against the requirements given in your requirements step. This way, when your character shows up in game, you have an idea of your intent and the capabilities of the character.
To answer what classes synergize well:
Non primary-casting classes tend to synergize well.
Given that most aspects of a level up are cumulative with prior choices (BAB, feats, HP) you want to avoid class features which depend on your level in the class. Therefore, avoid class features which have level as a variable within the feature.
Rages from barbarian are fine. You get more as you level up:
a barbarian can rage for a number of rounds per day equal to 4 + her Constitution modifier. At each level after 1st, she can rage for 2 additional rounds.
but you don't have the benefits of the rage reduced (proportionally to your compatriots) as you see in spells.
For the casting classes it's certainly possible to combine them in "gishy" characters (spell-slinging fighters) but they require a specific focus into the combination, preferably enabled by appropriate choice of prestige classes.
So, if you fail to raise rogue, you don't get as much sneak attack bonus damage, but if you're increasing fighter as the other class, you get a higher BAB to compensate.
Whereas a rogue would effectively be writing off "improved uncanny dodge" due to multiclassing.
Therefore, a good combination can be fighter/rogue, because each class brings a separate thing to the table, without having a significant opportunity cost for choosing the other. Other good combinations are those that lead up to exceptional PrCs, which combine features from both classes in useful synergy.
Based on the stats given, it appears to me that your best option is to not multiclass.
The most obvious option would be a dip into Monk, to get Unarmored Defense's Wis-to-AC bonus, but that would be trading leather's +1 for your Wisdom's +1. The other abilities wouldn't really add anything to what you already have.
Another option is Barbarian's Unarmored Defense. That would add +2 AC from your Con instead of your Leather armor, but simply changing to Studded Leather (also light, and giving full dex bonus) would achieve the same result. The Barbarian's Rage does add a moderately useful ability, but comes at the expense of delaying your progressing in Fighter/Monster Hunter.
Finally, a 2 level dip into ranger would allow you to pick a second fighting style, specifically "Defense" which grants +1 AC while wearing armor. Again, the Ranger's abilities do not synergize particularly with your other abilities, and delaying your main class abilities for 2 more levels is unlikely to be worth +1 AC.
Also note that none of these options combine. Unarmored Defense is specifically called out under multiclassing as an ability you can only get from a single class, and even the greatest Cheeselords still have trouble finding a way to be unarmored and wear armor at the same time.
It seems like you already have the best option figured out: take the Dual Wielder feat for the bonus AC, and indirect damage increase of 2 one-handed weapons.
While you're shopping for a second rapier, upgrade to a suit of studded leather. This and Dual Wielder will bring you up to 17 AC.
After that, just stick with fighter. At 7th level you can start using 2 superiority dice on damage, as well as automatically maxing superiority dice damage against certain types of enemies. At 10th level, your superiority dice get bigger by a step, becoming d10's.
These options will do more for you than you can get from any quick dips into other classes.
For a build like yours, and for most builds in 5e, multiclassing is a great way to increase the breadth of your skills and abilities, but usually does not add a lot to the depth of them.
As Ethan has pointed out in the comments, don't forget to turn to your teammates for assistance and buffs, as well as doing the same for them where you can.
Best Answer
Outside of the Wizard's saves, the consideration of the spellbook (as some DM's may have restrictions on buying your book as you become a wizard), and the character's history and background, there is no real advantage to choosing Wizard at first level if multiclassing as a fighter.
The fighter would lose heavy armor proficiency if multiclassed in to, and a high Con save has serious advantages, as you pointed out. The weapon proficiencies are a nice addition depending on character concept, but that is something you gain regardless of whether you take it at 1st level or not.
As for the cleric, they gain the armor proficiency regardless of what level if you choose an appropriate domain, they gain spells, and they promote normal spell progression. Overall, mechanically, I would say that Cleric is the stronger option. They aren't likely to do as much damage with weapons, but access to Cure Wounds and similar spells that are normally barred from Wizards is certainly a huge bonus.
If cleric is chosen, the choice of which class to take first isn't nearly as clear, nor is it as important.
Ultimately, look at the class features of fighter and cleric to decide which one you think is better for your goals. If you choose Fighter, it is advantageous to take it at first level. If you choose Cleric, it isn't really important which you take first.