Congratulations on your land purchase.
How much is your time worth to you? Smaller tractor with FEL and mower will scoop, lift, and mow but will take longer to do so than a larger tractor. Is the non-pasture part of your land forested? If so then a smaller tractor may be better for getting around in there. TC40 might fit the bill.
And how often do you think you will use a tractor? If you anticipate a lot of use then consider the ease of use convenience things like hydro transmissions and such. EHSS and hydros seem real popular with folks that do a lot of loader work. If use will be infrequent then go with regular gear transmission and use the saved money for more implements. Also, if you don't have much time to spend on your tractor then buy a bigger tractor so you can get things done faster ----- consider TC55.
If possible rent a tractor with a 5 ft mower and see how long it takes to mow that 15-20 acres. Have been there, done that myself with about 25 acres of pasture and a tractor that could barely handle a 5 ft rotary cutter. Was fun the first couple of times (because it was a new experience) but after that I wanted something bigger. For me it comes down to what you want to do with the tractor, how often you plan to do it, and how much time you want to spend doing it. The tractor I have now is quite a bit bigger than my first one; I'm happier now.
Keep those questions coming. The folks on these boards are always willing to provide advice and offer suggestions.
Good luck.