Glassing over old through hull fittings

Our "82 E33 has a couple of through hull fittings which aren't used anymore so I wanted to remove and blank them off before doing some bottom work this spring. This leads to a couple of questions about this project:

These appear to be original so from others experience, what sort of bedding compound was used and is there a change they can be unscrewed or should I start with a sawzall in removing them?

Once the fittings are out and the time has come to fill the holes, what do people suggest?
Will epoxy resin be compatible with the hull or should I use polyester to remain consistent with the rest of the hull?
For actually filling the holes, should I use mat in the inside and outside, or some combination of chopped mat along with cloth?
Would it be a good idea to cover the outside of the hole with wax paper or something similar to keep the liquid resin in place until it cures and then peel it off afterwards or would thins just make more of a mess?

In the end I don't suspect this is a very difficult task but I just want to make sure I do it right the first time around so any advice will be appreciated. Thanks!

Don Casey has described this very nicely in his fiberglass repair book. Get the old fittings out any way you can and clean off both sides of the hole with acetone. With an angle grinder, taper a depression around both sides of the hole (I think he said 12:1 taper) and build up concentric circles of fiberglass cloth wetted out with epoxy so that the last circle fits just a bit beyond the outer extent of the taper. Then grind it smooth once the epoxy cures.

It's a straightforward repair. The hardest part is keeping the exterior patch in place while the epoxy is setting up -- there's a tendency for gravity to pull it in undesired directions.

Patching unwanted thru-hull openings

Following the approach outlined above which I've also read;
Suggest preparing the inside surface first with the 12 : 1 transition down to 1/2 the hull thickness. Fit a temporary plug from the outside set in to align with the scalloped out area. Do the stage 1 process from the inside and allow it to cure. Then proceed to grind the exterior to the depth of the temporary plug and with the 12 : 1 transition (like a shallow crater), then build up the exterior. It would probably help to make a template of the hull curve to guage the amount of reinforcement you're applying as you build up the layers. Cure, grind to contour and ye're done.

I duct taped a small piece of formica to the outside to hold the shape of the hull. It curves with the hole. Put wax on it so the poly resin or epoxy doesn't stick to it.