Most of this has been covered, but I'll add my upsizing experience. I went from buckets to a 15 gallon corny with the dip tube shortened. First thing this required was putting a 12" collar on my chest freezer to account for the height. Next, I had to figure out how I was going to get it in there with it full. Since my brew stand isn't close to my fermentation chamber, I built a cart with casters on it and lifted the chest freezer into that. On brew day, I unplug the chest freezer with the 15 gallon corny fermenter in it and roll it over to my stand. I pump my chilled wort into the fermenter and roll it back into place.
Transfers from that point on are closed under CO2 pressure and easy as can be.
For cleaning, I just fill it up with hot water and oxyclean and let it soak for a few days. Pump out the cleaning fluid until it's light enough to lift and dump. Little to any brushing is necessary 98% of the time.
For a while, I used an airlock on a drilled corny lid. But now, I just throw a qd onto the gas poppit with a blow off hose going to a jar of sanitizer. I have plenty of head space and don't blow off anything other than gas.
Tank geometry on this scale has been a non issue. My beers have never tasted better.