its open sauce so you can modify it but I don’t think you allowed to sell it if your modifying it for your use I thinks that’s fine I would just check on their site
Yeah, I think you should ask the creators. I'm not sure if they would be okay with the idea, but then again since it's open-source, you're free to do what you want with it.
As long as you keep the copyright intact you can do as much as you can. I would recommend you to add as many hacks you feel like (some are absolutely amazing) and play with the template. Make a template in photoshop, slice and put it in the template system. Make it unique ... it's very easy...