If I were you I'd go with the space in the mall. More people tend to walk by and you wouldn't have to start off that huge. I just don't want to think of the upkeep costs of that huge building. But the general idea is great imo.
I wish you good luck with your project and will follow your work.
I'd really like to give you something for your project but I'm just getting into this whole crypto-currency-thingy.

Have a nice day!