More rust than I expected to find, Help Options

[Larry]

Purchased my first 914 a few weeks ago. I found some rust while looking it over but after taking off the soundproofing and really getting a better look, i found a good deal more rust than I expected. Looking for suggestions how to attack this. I have a mig and can weld a little. Was planning on building a rotisserie to do the work. If I had a better idea of how much rust I was looking at I probably would have passed on the car.
Would appreciate your suggestions as to how to plan and go about the work. How tough is it to do the entire rear floorpan on a unibody? The driver's long has a patch that is solid but I'm not sure what it is covering up. I can guess it's not too good. On the positive side I found over six dollars in change, mostly undre the e-brake. Thanks in advance.