Well, not every weapon because plenty of them share ammo types - two shotguns, heavy cannon and chaingun, plasma rifle and ballista and then BFG with unmaykr (hurr durr). As for enemy weaknesses it's mostly just plasma rifle for shields and it's a pretty damn good weapon in general with Heat Blast. And I did rebind them to be a bit more similar to classic Doom layout: 1 - Combat Shotgun, 2 - Super Shotgun, 3 - Heavy Cannon, 4 - Chaingun, 5 - Rocket Launcher, 6 - Plasma Rifle, 7 - Ballista, 8 - BFG. This way also all weapons that share ammo are next to each other.
The only one I don't use routinely is the ballista. I think I might have left 'C' available though, so maybe I'll put the BFG on that, put the ballista on 7 and make the rest more manageable. If it weren't for Marauders and Pinkies I'd probably rarely use the double-barrel.