Doctype Options for Different Company Branches

Hi, I’m developing a pawnshop management system. The company have different branches and I want the fields of my customized doctypes filled with data that corresponds to their doctypes automatically. I also don’t want to put a field where the user needs to select the branch. I’m thinking that I should create different site for the different branches with just the one instance that I have. Could I do it? If yes, how? And if you have a different ideas I would like to hear it. Thanks for anyone who would help.

Add custom fields. For a specific user, set a default value for Branch etc. via user permissions.