Cute design
A lot of the improvements I'd suggest are already documented as known bugs. I think it'd also be nice to allow bigger purchases once the waves start getting bigger (resource consumed faster, block produces more units, etc). Also, it'd be interesting if there was some way to control units better (waypoints?) since they often ended up in sub optimal positions. I did explore a lot of the map for fun during one wave, and it got me thinking it'd be interesting if you were required to send units to fight structures, or place additional resources out in the field to collect, or something similar to give an incentive to explore more. Otherwise, you'd just stick near the very start area.
Very nice game overall