Do you mean that you have to get more characters to unlock the shops? You don't. (Please correct me if I mis-understood you!I hear you have to unlock the shops when you make an additional character for your town.
No, you don't have to unlock any shops that I can recall with side characters. For example, I recently restarted a side character and was able to use Shampoodle from the start on that character.
The only things you need to unlock with them are specific services in shops that already exist, like talking to Sable to unlock the qr machine and buying coffees from Brewster to be able to work there.