You need some serious weight and power to move dirt, till and plow. Personally, if I were you I'd use the GT you have to mow the lawn and maybe blow snow. And then I'd buy a used vintage utility (smaller size, low profile) tractor like a Ford (600 and 800 series), Massey (135, 35), Case (430), etc. They're out there, they're relatively inexpensive, will last another generation, and can easily handle your dirt work that they were designed for. Plus, they're fun to use....

I have a Cub 2166 (the 2165's twin with smaller tires), and would never even think of using it to plow (dirt, I assume). I think this machine is smaller than your GT245.
You should have no trouble finding a good used tractor (assuming you have some place to store it), and since the mounts are universal (3-pt hitch), the cost of most attachments will be significantly less.

I have been leaning towards getting the Wheelhorse D-160. It has a 3pt, and seems heavy duty. Any one have any experience with these machines. It has the 16 horse onan engine. I am not familiar with these either. Any thing to look at to check it is in OK shape. Seems like the the 3pt and deck work, transmissions seems OK. The Deck is rusted through in 2 spots and needs some patches welded on.