Starting a restoration project Options

[JCHinCT]

I am starting restoration work on the first car I owned, a 1975 2.0L that I bought in 1979. Though it hasn't run since the mid 1980s. I finally got the car on a rotisserie, and I've just started a long slog to get the undercoating and seam sealer off.

I would appreciate some advice re metal prep. My plan is to eventually have the car media blasted prior to priming and finish paint. But in the near term I plan to attack each structural rust patch, and one-by-one weld in new metal, then hit each with some kind of primer. The goal is to protect each fixed patch temporarily while I go on to the next one. And since this process might take a long time, many months, I need to protect against encouraging rust on the newly patched zones. Only after I think I've got all the patch welds done will I take it for media blasting down to bare metal all over, prior to finish painting.

So here are a few questions:
- is there any concern about the type of temporary primer I use while the car is piecemeal patch welded? Or is it better to use some zinc or phosphate coating instead of temporary primer?
- I do not have a paint shop lined up yet. Is it advisable to find a shop that wants the job, and ensure I'm using a suface prep that is agreeable to the planned paint system? Or can that be dialed in just before media blasting? (I’m worried a reputable paint shop won’t want to deal with a car that they haven’t controlled through the media blasting phase.)
- any advice on getting inside the longitudinals to try to remove interior surface rust, and treat it, without actually cutting and opening the longs up? (I think a dumb question but thought I'd throw it out there anyway)
- similar question: after 15 minutes of shop-vacuuming, I think I see mild surface rust under the headlight buckets ... how do you get in there and deal with it properly?
- regarding sheet metal for the weld patches: I plan on 18 gage for structural areas, and 16 for non-structural ... but plain old low carbon steel? or should one aim for something with a rust-preventative coating on it - even though it needs to be MIG welded?
- I found some horrible rust in the front trunk compartment, under the seam sealer on the driver's side. Rusted through, with a couple of index-finger-sized holes. Obviously, this needs to be totally removed and creative weld-in patches made. However, in other places the seam sealer looks really solid with no sign of the "rust-crunch" sound underneath. Option 1: just leave the “good” seam sealer, and later media blast it and paint over it. Option 2: dig it out even though its probably fine, assess the metal underneath, and then later apply more seam sealer over it before painting? What do you think? This is especially a question at the rear shock towers, that seem almost like they're new and almost certainly rust free (though, how really can one tell without digging in?)

Thx in advance.