It is unfortunate you had encountered a game crashing error(I assume it because I change help text which is written in array, but forgot to update array size)
I am happy you liked the game concept and art.
The difficulty can definitely be a problem, most of feedback I received was on graphics(which helped to improve them a lot), but most of the people do not spend time playing more then one level thus balancing levels is quit hard.
I was thought about preset torture devices. But I decided let play find their own strategy how to spent starting money. Your idea about starting with preset stuff based on difficulty sounds interesting.
Sorry I didn't quit understood your second statement, about button.
I was thinking experienced players would know that tower defences usually have tower upgrades, and new players will just click on stuff out of curiosity. I'll attempt to make much better tutorial. Could as well split it in two parts, for beginners detailed tutorial and for experienced player only unique element.
Thank you for playing and giving a valuable feedback.