I've never run a multi terrain loader, like the 257. The only skidsteer that I ran was a Case 75xt, it had more than enough power, but because it was on wheels it was not the best for grading. I have wondered if a machine like the 257 or something comparable on tracks would be better. One of the things that I like about skidsteers is their power to weight ratio, for example the 257 weighs about 7,600lb and is around 60hp, while a Komatsu d21 is about 9,000lb and only 40hp. One of the things that concerns me is traction with 257. Like I said I haven't run one, but the tracks don't look real aggressive, then again looks may be deceiving. I do like the idea of being able to move the equipment yourself, paying $100 each way for delivery gets old fast and you are limited to their schedule. I assume that you aren't planning on digging foundations or anything like that, but mainly landscaping. A tractor with a various attachments and a skidsteer sounds like a good combination for the type of work you plan on doing.
We used a d21 and a landscape rake pulled behind a four wheeler to do our lawn and it looked incredible when we finished. They do make a 6 way blade for skidsteers, but I don't know how easy it would be to use.