Nice game. I have found it a bit fun. Unfortunately there are some bugs too (as you wrote in the description). Hope you will fix this in the future and balance the game too.
SPOILER:
How to win? Upgrade coins gain. Up to 50 per enemy. (some other upgrades too, but they will be cheap and you will have money). And when you will have ~10000 money per round spend it on shooting speed and some damage. One tower per map will win the game.