I have to agree with some of the other people here, the rules are not very well explained. There should at least be 1 tutorial explaining how to deal with black hexes.
I agree with LucV3. While it may seem to be a better investment to save your gold, it's a lot more efficient in the long run to upgrade all heroes that you can.
I hired a Donut Shop manager before I actually owned a Donut Shop, and then when I bought the shop the manager didn't work. This is a glitch that needs to be fixed.