Lots of good advice. Here are just a couple more things to think about.
As you've found, used tractors are a little hard to come by. That's not all bad, because if you find one and don't like it, you can usuallly sell it for what you paid. There are some real good bargins out there if you are willing to do just a little work.
Over the years I've bought and sold a number of small tractors that mostly just looked awful, but were in good mechanical condition. The Yanmars are my favorites because they are such incredibly simple tractors (but absolutely no frills). Parts are readily available at reasonable prices. But, they are not for real big people. As was mentioned above by MotorSeven, they don't have a lot of leg room.
I've had too many "classic" tractors (Ford N series, Allis Chalmers, Massey's, others built before 1965) to suggest them to a newbee. I'd also only really recommend a diesel. On the older gasoline tractors, it seems you are forever having to clean and readjust the points, the carburator, etc. The diesels just need clean fuel, an oil change at least once a year, and a little grease now and then.
Also, if you buy used, buy a tractor that has been in use for at least a year. Don't buy one that has just been "reconditioned" by a dealer or importer. There are way too many of them that are nothing but trouble.
Tractors in the 20 - 30 hp range generally get 50 to 100 hours of use per year. Be wary of anything with real low hours on the hour meter. Most diesels in this category can go at least 2500 hours without major engine issues.
FELs on small 2WD tractors are not worth a darn. They are even worse on a 2WD without power steering.
Buy something. Use it for a year. You might even beat the heck out of it while learning about tractors. Every month do something to it. Add a little paint, put on some new decals, etc. You should be able to sell it for several hundred more than you bought it for.
Also, if you are looking at new tractors, don't just limit yourself to Kubotas. Most of the tractor brands are pretty good. Good local support for a new tractor is probably more important than the color. You can learn a lot about brands from reading the many postings on this website.
Good luck,
Knute