One thing I've heard in these forums over and over again, and it something that applies to me very well: the biggest mistake you can make is to get insufficient power and features. I just bought this 5 acre property last year. Before that, I lived on a cookie cutter lot in the city (45 feet by 140 feet). So, I had never needed anything bigger than a 3 HP lawn mower (the kind you push). When I got out here, I figured the JD riding mower would be good enough. I was wrong. I paid $2500 for it last year and consider myself lucky to have gotten $1,500 as a trade-in this year (right after I traded it in, I saw the exact same model, brand new, sitting at Home Depot for $1,999. So, in a sense, it cost me $1,000 to learn this lesson. Part of the reason I took two steps up (from the 1500 to the 2230) is that I did not want to go through that again. In fact, I took three steps up, because I was originally looking at the Simplicity Legacy XL, and my wife talked me out of it because she wanted me to get something that would still be enough in five years.
By the way, the reason I didn't go any bigger: low center of gravity, and weight. I didn't want to be high off the ground on my hills, and I didn't want to be tearing up my lawn with a 2,500 pound tractor. So, I opted for about as much power as you can get in a small and relatively light package.