Well it looks like you have been given some pretty good advice already, I would emphasize keep reading and then asking questions. A few simple abbreviations or term: FEL Front End Loader, 3PT Three Point Hitch, the hitch attachment point on the back of the tractor that implements fasten on to. QA or Quick Attach, or SSQA Skid Steer Quick Attach, means the attachment plate on the Front End Loader (FEL) to allow you to quickly remove the bucket
of the FEL and put some other attachment on, like a set of pallet forks, or round hay bale spears. The Skid Steer part is because they were originilly developed for Skid Steer Loaders (think Bobcat) and they are a standard. There is also a Quick Hitch that goes on the 3PH (back of tractor, remember) that allows you to hook your 3point implements quicker and with less swear words. There are several brands of those, and different schemes, like John Deers I-Match, Pats Easy Change, Carters, etc. Now we come to tires, R1 are Agricultural tires. with a very aggresive tread, R3 Turf tires like on a garden tractor more or less, and R4, Industrial tread, like you would find on a backhoe. You will find a large difference of opinion here on the best tires to have on your tractor, bottom line all tires are a trade-off, you must select the type that fit your terrain, and type of work best. I find that the R4 Industrial type are a good trade off for me. Now comes the transmission selection. there are many, from simple Gears, to Syncronized Gears to Shuttles, in many flavors and brand names. I prefer the HydroStat, for many reasons. But like tires (or even worse) there is a huge difference in opinion on this, but I urge you to drive a hydrostat equiped tractor of any brand before you buy. I think it makes that much of a difference. Now as to buying used, I wish you all the luck in the world, and many here have had good luck at finding a good used tractor at a good price. I did not. I searched for several months, and all I found was worn out junk, and good used tractors at near the same price as new. My first tractor was new, at above the price I had budgeted for it. I got a lot of use out of it, and later traded it for a another new one, just before the Manufacture went out of business. (Long) Be carefull, You cannot go wrong by sticking to the major brands, I happen to like Kubota, But I would not hesitate buying any of the major brands, and even some of the second tier promising up and coming brands. But think it through, and find a good stable reliable dealer of the brand you are interested in. Bottom line is just keep posting, and asking question, and we will all try to help as best as we know how. Like anything else you are going to get differing opinions on a lot of the subjects, but you need to look at the overall response and form you own opinion.. Thanks and good luck.
James K0UA