This is a brilliant idea for a game, and one that fits especially well with the jam theme!
On my first couple tries, I played this like a typical tower defense game, stacking defenses at the front and moving back. But then I realised this makes it too hard to collect resources due to the bullet hell. This simple design tweak makes the game much more interesting and you need to think extra hard about where to place towers.
The visual style is really nice, the gameplay is smooth and intuitive, and the game is paced nicely! I'm really impressed with how much you put together in only 48 hours, great work!