If possible it would be great to have the zero-turn mower plus a tractor of about 40 hp. Small tractors of around 20 to 25 hp can be used for finish mowing, but they aren't as good as the zero-turn mower for a finished lawn look. Larger tractors can be very difficult to maneuver around trees, shrubs, etc. in a lawn situation.
Also, a 20 to 25 hp tractor would be undersized for the rest of the property, although better than no tractor. In my area, a good used 40 hp class tractor can be easily found for $5000 or less. I bought a MF 55 hp tractor 25 years ago for $5000 and that's about what it would sell for today and it runs just as good as it did 25 years ago. Whatever you decide, buy a diesel powered tractor.
