Okay, here's the cool (though rather useless) information obtained by way of FFXITool.
Note: you will have no way to access almost any of this data - it's in an area that was used by the developers for debugging Chains of Promathia missions as they added them. (For those of you with FFXITool, it's the area numbered 6630 for text strings.)
2nd Note: they may have changed things from after this testing mechanism - however, these should be fairly accurate anyway.
* There are only three faces for any given race; these apparently determine the conversational style of the NPC, but nothing else.
* The NPC can be kept out for as long as 50 enemies' worth of fights - whether this is controlled by leveling it up or otherwise, I don't know.
* The NPC can end up using any sort of weapon, but only melee weapons. (No ranged attackers, unfortunately.)
* There are multiple levels and types of equipment given:
- Weapon: 2 levels, 1 type.
- Shield: 2 levels, 1 type.
- Headgear: 2 levels, 1 type.
- Body: 3 levels, 4 types.
- Hands: 3 levels, 4 types.
- Legs: 3 levels, 4 types.
- Feet: 3 levels, 4 types.
This would seem to make for 256 distinct armor appearances, and roughly 166,000 distinct gear SETS assuming no changes made in weapons. (With weapons changes, it's over a million distinct gear sets.)
* There is a "pop time" field which can be adjusted between 1, 5, 10, 15, 20, 30, 40, 50, or 60 minutes - I don't know if this controls the maximum amount of time they can be out and idle, or what, but it's definitely interesting.
Hopefully this information proves to be moderately useful. :-)