Yeah, I'm currently working on figuring this stuff out. Thank you for suggesting Creative Commons, I took a look and wasnt too sure about any of them but I'll keep looking.
I don't wanna commit to anything without being sure first. I'll probably put together a little FAQ at the very least this week.
What I can tell you is that you're free to use it in as many commercial projects as you want and you can edit it as you want. The only thing you can't do is sell or redistribute the tileset itself in raw format. For example: lets say you build a map creation tool for your game, you need some way to protect the png file so that way people can't just go to the editor's folder and grab the file and start using it themselves for their own projects without having to buy it from here.
Hopefully that asnwers most questions? Let me know if theres anything else you'd like me to clear up