Amp repair...What to expect.

Replacing parts WILL be a great challenge. These amps aren't supported anymore by the manufacturer for long time already. God only knows who possesses schematics as well if the problem will rise more complicated. Assembled boards to replace aren't manufactured either so exercise safety and protect your unit with surge protectors. There are also not too many of them for sale either as they become slowly the legend of hi-def audio.

You've raised some issues I never even thought of.
Roland at carveraudiorepair has cornered the market on all
parts, but when I needed service it was a 3 month wait. On the forums I found out that he has former Carver/Sunire people with him and the schematics and such.
I went to Vintage HiFi in Pittsburgh (an authorized dealer and service for many years). Very nice owner, my only worry is the quality of the parts used.

Yes, they are in great demand. I'm sure you've followed the sales on ebay...they are snatched-up very quickly.

anywhere from 300-500 hours to break-in.

It's not break-in it's parameter settling of mainly large signal components such as power transistors and it's not 3 months worth of listening. It's substantially shorter at least audibly. 25...50 hours is more realistic.
Leaving unit on stand-by for a few days will also do the trick.

Mine took 50 hrs. to start sounding like a Sunfire again. Then at about 300 hours, it opened up and sounded like its old self (except that now it was dead-quiet).