This is incredible, it looks and sounds great! The only issue I can see with it is that it's too easy to essentially soft lock yourself, on my first run I prioritised upgrades but then didn't get to buy the knight before stage 5 so it was essentially unwinnable, on my second run I was 25 coins shy of buying the tank when the enemy stared making them, so that was pretty much unwinnable. It doesn't help that the browser version seems to cache my progress and I couldn't find a way to erase it so I had to go to in-private browsing for the second run. It would be nice to have options to salvage a run (being able to grind previous stages a bit or respec into different upgrades) rather than having to play through from the beginning to make different choices.
Overall though you should definitely continue with this, it's super novel and engaging!