Yes the HP tuners can be used on multiple vehicles. It's big in the GM world. You do however have to buy credits for the cars you want to use them on. So even after purchasing the tuner you will be required to pay $100 for each vehicle IIRC. Someone please correct me if I'm wrong.

Scanning isn't mandatory but helps you keep tabs on the car and is always a good idea.

As far as your fox goes. There are a few of us around here that enjoy them. I've got a 85 coupe with a 87 EFI F-150 block.