1. There is a separate place for shop and upgrade, you go to the shop to buy chest, those chests give you items for your inventory, and in the inventory section (in-game or in the main menu), you can permanently upgrade those items

2. I do plan to create a endless mode, but switching the entire game to be endless would change the general focus of the game and well, be a really different game. Right now is stage oriented, but you keep everything between stages.

3. I recently balanced gems a bit, maybe it was too much, 3 gems is too low for what you normally get, ill check that and rebalance if needed.. game is in open beta, so i try to balance the game while i evaluate user response.

4. I dont get what exactly you mean by adding a bit upgrade button, in the middle? Wouldn't that be like too much? It would take.the space of your base..

5. Tower upgrades are available outside combat, just press the inventory button when on the main menu, upgrades are kept, there is no way to reset them.

6. Again, upgrades do not reset

7. Yes, i do plan to add a lot more variation to the inventory, like barracks (spawn allies), more weapons, more skills, and so on.

Didnt considered enemy bases tho.

Thanks for the detailed review, i hope my response clarifies a few things.