I love what you are saying. Consider it done because I've started an automatic wall placement and slowdrone started to make our treasure chest.
Refunding of half is something possible. My implementation of gold needs to be improved to allow that (for now, it's your selection that's carrying the gold you'll use)
For the wave start button. I've not thinked of it. As you'll be bocked if you have 0 gold it can allow you to take your time to build the dungeon without making the game too easy(once balanced I mean).
I add this to our road map.
Thank you for your interest!