Plague Bringer:
This sounds like a cool idea and again puts me in mind of Tribes, where players had packs, deployables, buildables, reactors, armouries, armor classes and etc. When a player logged in, he could create as many accounts as he liked, but each kept track of certain statistics. What you are describing sounds very much like (as you said) Halo, Warrock, GunZ, and Tribes. Again, I would think that the Torque engine would be of service here (since similar things have already been done with that engine). Hope this is of value to you.
P.S. I have an idea for a mod using experience points to unlock certain classes, 3 guildtypes (projectile, energy, nanobiotech), 9 classes, possible 3 faction option, multiple gametypes, etc. It's not on my new machine, but I'd be happy to type it back in if you want me to e-mail it to you for your amusement and perusal. It's pretty extensively thought-about (if not thought-out) for a person who will never code it. It's just sitting there rotting away, if you care to take a look...