As far as the corrosion, use a wire brush on the bronze thru hull, You will quickly see the condition of the through hull. If the bronze looks new under the corrosion, it is fine, if it is pink and brittle, get ready to pay up to $800+ per through hull to replace depending on the quality you use. If one is seriously corroded, the others might be as well.
As far as bonding, you will hear different things. Some are concerned that in a lightening strike, if the through hulls are all bonded, they will break and the boat will sink. If some are bonded and some are not, probably the strategy was to bond every piece of metal within a certain diameter of the mast
The through hulls are not the ground, the engine
block would be the ground.
for bottom paint, ablative paint can generally go over anything. A quick way to tell if you already have ablative on there is to swim under the boat with a coarse scrub brush, start to scrub and if you see a plume of paint in the water, it is ablative or "soft" paint.
Once you pull the boat, try to determine if there is a thick build up of paint. If so, you may need to strip the paint which can be a big project
Take a few pictures and post what you have questions about.
Good luck and make sure you have some extra $$$ for unexpected things.