'85 245 GLT - how much rust is too much?

Howdy! Have been getting into fixing my old Volvo recently. Had a long illness that kept me from maintaining her well and she's worse the wear for
it. Amazed that the car still runs with all the years of neglect and abuse, but am having fun learning and fixing and the car's responding well to the repairs. Have been replacing essential engine components to get her running well again. After 230k (estimated - odometer broke at 187k years ago), a new exhaust system and a tune-up has her purring like she did when I drove her for the first time (well, except for the vacuum leaks that I'm going to fix this weekend). Am putting in a new wiring harness and new suspension components (bushings, shocks, springs) to make the ride nice again, too. It dawned on me recently that the brown holes in the car were kind of important to learn about. Don't have any experience with rust, but figure it's something I should probably pay attention to before I sink scads of dough into the restoration of my trusty, reliable work-horse. There's some rust on the rear quarter panel, below the driver and passenger doors, around the windshield and some small spots on the roof. The areas below the doors are large - 3-4 inch holes. The wheel wells are clean and rust-free. The undercarriage looks good, although some components have lost their paint and have a nice orange coat on them. I've cleaned and painted a few parts and will either do the same for others or replace them, but the body has me kind of nervous. Any advice or input appreciated. No matter what, I'll do the minimum required to keep the structure sound and air-tight and drive it till it falls apart.
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