Also, may I add my two cents here? I think customizable weapons would be a rather good idea (especially with cryengine, because it already has an attachment system that we could take advantage of) personally, customizable weapons have been something I've always wanted in a halo game, so things like different ammo types, grips, scopes, flashlights, butts, ammo counters, etc.-snip-
Weapons will NOT be able to be customized (scopes, grips, heavy barrels, what have you) YET. Everything will be based on your player stats.
As for armor. I think that armor shouldn't effect stats. Once we start assigning stat bonuses to armor parts, we almost steer players to certain armors depending on their play type, rather than what they want to look like. So by assigning + agility to H4 variants, and say the player wants to play more as a tank but like a certain H4 perm, he won't get to play the way he wants because the stats are limiting him. The only restriction would be that Spartans can only wear MJOLNIR, marines can only wear marine armor, grunts can only wear grunt armor, etc. etc.
So to sum it all up, damage and stamina and all that will be solely decided on player stats. By leveling your character you can upgrade your health, damage, etc. and your class bonus adds a little extra. -snip-
Also in regards to armour types: How deep would we want to go with armour? Personally, I am all for different armour pieces giving different perks, but limited, in a sense. For example, if one player picks out, say, the h4 recon helmet, that might give them, say, extended radar scan range or something like that, but there would also be other armour pieces that have that same function, so it's not solely that armour piece. Also, maybe we have ways of installing the same things into different armour pieces? So if a player wanted the radar scan range bonus from the recon helm, they could take that, and plug it into, say, the halo reach MkV helmet, but it might need a specific skill to modify armor pieces like that.