I believe a lower end residential ZTR will work just as good as the expensive ones. It's just that they aren't going to hold up to the wear and tear as well. If you're only doing 1/2 acre per week, save your money.
I've heard the statement many times that ztr's are terrible on slopes. My personal experience is the opposite. My property is mostly flat, with the only sloped areas being where the property meets the road at the lot corners. These areas are about 5'-6' below the road surface with the hypotenuse being about 10'-12' in length. Don't know what % grade that makes it as I don't feel like dusting off my trig. Anyhoo, I own a Dixie Chopper Silver Eagle with Turf Boss III tires. I can stop, back up, turn, drive up, down and across while on these slopes without any traction problems whatsoever. I will say that these tires can be a bit of a double-edged sword in that when the ground is really wet, any semi-aggressive turn will tear the turf up pretty good. When it's dry, no problems at all.
I have a Ferris ZTR and a Craftsmen. I will use the ZTR for everything EXCEPT on the slope that goes down to my lake. It just does not feel as stable in that situation.