On the overheating issue, my 1984 P30 454 coach was always overheating on hills - the fan clutch was working but after so many years the radiator was clogged. I had it rebuilt and upgraded - the old one was 3 core and the new one was 5 core. Slightly thicker but fitted just fine. Never had to worry about overheating ever after that, and I pulled grades in the CA desert at 115F towing a Jeep GC so it was well worth the effort.
Flat spotting is caused by sitting still and not be hard braking.
It will be noisier than some other coaches and insulating the dog house will help as will fixing that exhaust leak - for one thing, you don't want poisonous exhaust gas entering the RV, but also temps and other damage will be affected by a leak. 454s are better than 460s and use a gasket (460s don't) and so presoak the bolts in anti-seize for a couple of days before attempting to remove - a good repair shop will use an acetylene torch to heat them up before attempting removal.
I have repaired my own ac on several occasions but you will need to remove it all to flush it out properly and replace the compressor and the receiver/dryer - the good news is that it's all pretty easy to get at on an RV :) Shop around on eBay for the parts and save $$ over dealer.
