I'm not sure what I should expect to pay for rent. What percentage of my sales should rent account for?

You really can’t know what your sales will be projected at until you find an appropriate space that is suitable for your concept. When you find the best spot for yourself, then you need to determine what your sales should be, and if it is feasible to achieve that goal in that space. Ultimately you’d like to see your rent at between 5 to 8 percent, with variations depending on your area.