Not sure the type of restaurant you are planning, but I wish you the very best of luck and success.
My mom cooked mostly Italian food but for American food what I miss the most (or what I don't think the UK gets 'quite right') are all kinds of fantastic salads, cheesesteaks, hoagies (can you tell where I'm from?), pumpkin pie, pumpkin ravioli (don't know if that is American

), collard greens, veggie-rific anything (as I just don't see a big variety on menus here), cornbread, baby spareribs, club sandwiches, chili, apple pie, crabcakes, GOOD baked beans, turkey potpie, coleslaw, potato salad, real baked macaroni and cheese, pasta salad, bagel sandwiches, mmmm.... I'm hungry!