Any zero turn is not going to handle the hills, once they start sliding you're basically just along for the ride. A stander is better for hilly property but still you'll have issue and standers are made for people that are 5'8" for the most party. They kill my back. What will work would be a hydrostatic walk behind with a TWO WHEEL velke that you stand on. You can ride it most places but when the hills and creek banks come into play you can step off the velke and run it as a walk behind and do more than you can imagine on hills. On the creek banks you'll have to keep your distance and break out the string trimmer, at least until you get real familiar with it.
Heres the walk behind I'm referring to.
Turf Tracer S-Series 36, 48, and 52-inch Walk-Behind Mower
And Velke
[VKX2]