Thanks! I played some more and got pretty closed to 7 towers, maybe 9-10 or so, good to know there's a way to push even more. I definitely started seeing some value to ÷2 when trying for minimum towers. That kind of "win strategy" reminds me of Zachtronics game goals where you try to win with lowest cost, lowest area, fastest, etc. Could be a neat mechanic for your levels.
Showing cooldown and visibly showing a tower firing would both be quite helpful.
I hope you continue developing it, the unique premise offers a lot of opportunity for interesting game mechanics. Good luck on the game jam!