Thanks for the feedback! Yeah, I wanted to set it up in a way that the player wouldn't really want to just fire freely, but I'd have to agree with you that having it set up with a mouse instead (or as an option even) would have made that both easier and probably more fun. I was kind of going for a classic 8-direction style with it, but the mouse would have fit the game better.
For replenishing your energy (health and ammo), you will regain a portion of it back after each wave of enemies.
As for the funds/score, the purpose of that is to replenish your energy at the space station. To get there, you have to pause ('P' key) and then select the option to retreat (but you need to have at least 25% of your energy (explained in game to be the amount of fuel it costs to make the trip back to base)). Then you'll be at a screen where you can return to the game, resupply ('Merchant'), or quit to the main menu. This is a common response I've gotten, so I'll look into making that clearer in a future build.
The final score page has a little bug where it uploads your score, but it only takes the score from the last time you were back at the base. It's a really simple fix that I noticed right after the deadline. It should project the amount of 'funds' you have when you die, but I just forgot to carry that information over there. So yes, it is based on how many enemies you kill which equals your funds, but you can subtract from your funds to replenish your energy.
Ah yes, the enemy models... I so badly wanted time to throw something together for them, but I just didn't have the time in the end. I almost recoloured the player ship and used that for the moving enemies, but I came across some issues with that too.