It sounds like a wonderful idea, but hear me out on my suggestions.
Everytime a new game is released on the network, that's where the real sweats come out, or the people who seriously play overtime to gain these "credits" as you call them. As long as you keep that in mind, and think about some of the more casual players, you could alter the credit amount so that it's not too overpowered or it's not enough if you're on a losing streak. It's just a balancing act.
The maps for this could include such features and points that you could easily overcome with a specific tool, like the axe or pick on a certain wall block, and maybe special blocks that you can place down that make it hard to travel through. Also, we still have to consider about the regular corridors. If there was, let's say a hacker in the lobby, we want the course to be close knit to keep them so that they actually have to fight, but we also want room for them to be able to run away and regroup.
Lastly, the more ambitious thing. Kits would be nice to have more of an individuality to each player on each team, but it may overbalance the game if you get one factor too overpowered.
Theoretically, if executed well, this could be a great gamemode that would add to the server even more than usual, because my friends love those kinds of games.