Thanks for playing!
As you say the game currently lacks a lot of content since it's just a prototype, so a lot of systems aren't in yet. The amount of bullets you can spend will be possible to increase via upgrades mid-run, however part of the strategy is to try and use your shots sparingly so you're not caught without when you need them. It's in a bit of an awkward place difficulty-like right now because I only had time to make two enemies for this prototype, but you'll be seeing tougher enemies and upgrades before going on for this many rooms in the future.
Doors were initially added as perhaps a way to transition levels, but for now I've skipped on having them work that way since currently there's nothing to do in a level after clearing them, and not sure if there will be. Movement speed isn't exactly high so if you have nothing to do in a room after clearing it and the doorway is at the other end, I feel it's better to just cut out than to waste time.
Thanks for the compliment! I don't think the camera can be any closer during normal gameplay though due to how the camera needs to be static and encapsulate the whole level. There will however be other types of scenes where closeups might be possible, such as shops or character selection.