Within a match, I want my players to be able to go around picking up weapons, armor and usable items. Essentially "leveling up" by collecting them and using them to overcome other players. This gives variety and I imagine some players will have stories of how they managed to get a set of X or Y before being killed.
If they lose their advantages upon dying(like in most multiplayer-FPS) most of us wouldn't call it "leveling up"
(It's better this way though)
2) I want my players to have a sense of progress outside of a match. (again without grind and imbalance)
I want my players to be able to look at all the matches they have played and see the abilities, items, classes etc they have unlocked through playing these matches. Also, it allows me to "slow roll" my content, enticing the players to play to unlock new content and getting excited about future content.
If i may recommend, make a whole bunch of skills, let's say 50, let players unlock 5(10?) when they start the game,
when they play a match they 're allowed to pick 5(10?) skills they 've unlocked,
let them unlock more skills as they "level up" yet they still get to pick 5 (unlocked) skills when a match starts.
The only skills that would have some kind of prerequisite(aka being level 30 before unlocking it) should be skills that you do not want to confuse newbies with.
(This is a bit stolen from the LoL's skill-tree, they got two ways of leveling up that work approximately like this, maybe look at them)
3) I want to monetize.
The project, currently under developing, is a small free experimental game hosted on a server that I am paying for. But I want to have the option to ask for some donations to keep the server running or expand in the future. Being able to sell special items will help me do that.
Skins for characters, items, and whatever you can throw a skin on ;)