Nice looking 914 to start with. The best bet would be to try to locate a member here familiar with the rust issues on our cars and get them to inspect it for you to give you a general idea of how significant of a rust problem you may have.
To make that easy, if you can, pull out the seats and carpets so you can check the floor easily for rust-through. Maybe pull out the back pad to see about rust along the bottom of the firewall where it meets the floor. Check the suspension mounting point in the rear where they attach to the chassis for rust and metal fatigue. Pull the battery out and using a nice bright light and a metal probe check the "hell hole" for penetration from rust.
The more you can do yourself, the better off you will be in your pocketbook. You can post photos and people here will chime in. Start searching now for a shop that is very familiar with 914's and the typical rust repair they typically require. But be cautioned, you want someone who is a known 914 metal-man. A lot of people will talk big but have never done the actual work and will try to learn on your dime as they go. Or maybe they were great body men a decade ago and their circumstances have changed. Once you find a shop, hopefully at the recommendation of fellow club members, go visit the shop in person and look at it and the work in progress on other cars. Hopefully they are all old Porsches and at least 1 is a 914. I would not be afraid to look outside of your immediate area to find a good shop but try to keep it close enough so you can actually go to the shop in person.
I would not rush into this process. Take the time to make informed decisions and know the path in front of you. Have a solid plan for repair work with a budget already available.
Finally, starting with a solid, rust-free, (to the extent possible) chassis, is the best way to own one of these cars. Fix it once, fix it right, and never have to deal with it again.
Good luck and enjoy the ride.
Michael