I think the question you want to ask yourself is how you expect to see the system used in play. There are a lot of systems, FATE included, which have as a fundamental feature that every attempt by player A to hit enemy B results in a die roll. There are an awful lot of variations on that concept, but you'll find the same thing to be true in a really overwhelming number of systems. This is fine for tabletop play, where a die roll takes a few seconds and is kind of a fun thing to do in its own right.
But imagine that you're running your Borderlands game on the forum. I played Borderlands I, though it was a while ago, and I'm pretty sure I remember it being almost constant gunfire. Which is great for a video game, of course. But do you really want your players to be rolling a die and adding some numbers for every attempted gunshot? When you're doing that over a play-by-post system, you're now looking at a single combat potentially stretching over a week or even multiple weeks, based on the posting speed of your players.
I know right now it looks like you're focusing on character creation, which is fine. But what I'm saying is that you should project forward to how you want the system to work during actual play. Nail that down, then work backwards to figure out what character stats you might want or need. You might find out, for example, that there's no point distinguishing between "Heavy Weapons 3" and "Heavy Weapons 5" or what have you, because you don't actually want to run the combats themselves with that level of detail.
Here's a gut-simple system that I'm just making up off the top of my head, just to give you an idea of what I'm talking about: [Ebb's Incredible Simple Combat System, patent pending]
- Every character has a skill called "Fighting". This ranges from 1 (a non-combatant) to 6 (Rambo). If you're wounded, you're at -2 to your skill, minimum of 1.
- When there's a combat encounter:
1) Work out in your head what the bad guys strategy is going to be for the fight. If you want to keep yourself honest, write it down.
2) Ask the players to give you their general strategy in the upcoming fight. (ie Joe's going in blasting, Sarah's going to snipe from that hill over there, Bob's going to try to circle around and flank them from behind, and Ed's going to hang back and run in with a medkit if somebody gets hurt)
3) Based on how well 1 and 2 match, come up with an 'advantage' number for the fight. This could be for either the players or the bad guys.
4) Add up the good guy's Fighting skills. Subtract the bad guy's fighting skills. Add or subtract the advantage number. Roll some FATE dice (this gives you a number from -4 to +4) and throw that on top
5) If the result is:
-10 or below, players all die. New game
-9 to -2, players lose, end up captured / wounded / stripped of equipment / some other bad end
-1 to 1, tie game, everybody backs off. Try a different approach
+2 to +9, players win, but end up with some injuries or equipment loss
+10 or above, players win decisively, bad guys all dead or captured (depending on what the players want).
- If the players win, let them write the long description of the battle and what happens. Give them enough information about the bad guys that they can do this.
- If the bad guys win, you write the description.
Now that's probably not workable as-is, but I hope it gives the general idea. The point would be to focus on one roll to cover the whole combat, and play to the strengths of forum-based play, namely the ability to write long detailed descriptions. Avoid the weaknesses, which are the long turn-around times between players contributions.
I hope that the general idea there is clear, at least. It's great that you're excited about the setting and that you're finding players who are too. So don't get bogged down in the system side of things to the point where that energy gets sapped.