ghee22,
I just realized that we actually didn't address your actual question, which was should you run your "main PC" as local user or admin. Here is the answer:
You do not even have to log on into the computer to make SQL server runs. SQL Server will be running as NETWORKSERVICE or SYSTEM account.
SQL by itself has a built in backup function but you will not be able to access it. He can set any account with adequate privilege to copy these file out with having to use Admin account.
Just follow general rules of thumb on server security. Do not use administator or high level account unless you really need to.
I can help you with this.
