I'm so sorry, I didn't notice these questions until today!
1. The building options don't have a lot of variety, sadly. At the time I created this I was struggling to come up with what to draw for that, especially since there's not a lot of room to work with to create obvious variety. Going from memory, there's a few options for towns/villages, including one with a dock. There's one type of castle. There's a bridge. There's a mine opening. There's also a variety of dots and flags so that you could use as an alternative to indicate locations. I don't mind expanding on this, so if you give me a nice list of things to add, I'll draw them.
2. Yes, it's set up for RM, but it can be made to work with Unity. I'm just not familiar with Unity myself so I don't know the resource standards.
3. Absolutely, edit it however you want, hire someone else to copy the style to add things in, whatever you need to do to make it work in your game. I don't want edits shared outside your game making group, though.
I hope that's what you needed. Thank you for your interest. Again, I'm really sorry I didn't respond quickly.