Before using the compressed air put a bit of wood about the thickness of your disc between the pistons. This will stop you blowing out one piston completely leaving the others firmly stuck in place.
Otherwise the job is simple.
The scuttlebutt is that separating the caliper halves is a no no and should never be done. I can’t work out the logic of this, and always split the calipers to replace the channel seals as well, which can be bought from any brake place once you actually know what to ask for.
Depending on your degree of paranoia you might decide to replace the bolts that hold the calipers together with new grade 8 ones. I sometimes do, sometimes don’t. Do NOT use stainless steel bolts, only proper grade 8 steel. If they are black you can plate them safely.
Don’t sandblast the mating surfaces of the 2 halves and mark the calipers prior to disassembly so that you reassemble each pair correctly.
Sandblasting inside the caliper is otherwise fine as the important hydraulic surface is on the piston. Inspect the piston surfaces carefully. Tiny imperfections can be polished out if they are not directly under the seal surface, but if you find anything worse than that you should replace the affected piston(s).
Plate the calipers halves separately. The few microns of thickness of zinc will not adversely affect fit. To be honest though, I have gone to painting calipers as the zinc finish quickly deteriorates over time. There is no reason of course why you could not zinc plate them and wait and see and paint them if you are unhappy. You could also clear coat them with an appropriate paint after the plating.
Plate the bleed nipples and other mounting hardware at the same time. I have actually plated the short caliper lines in the past too but some disagree with this. The car I did that on is still in regular use nearly 10 years later without incident. These days I usually make up new pipes whenever I do a major caliper overhaul.
Getting the piston to go through the seal for the first time can be difficult. Use lots of rubber grease.
You may as well get your discs skimmed at the same time. Have fun.