Sparky, not being a smart arse here, but I really don't think you'll be ultimately happy with an old used tractor like you say. It sounds like you are well ahead in life in your thirties, and I can tell you seriously, every nickel you spend fixing a worn out $5,000 tractor, you will beat yourself up thinking about lost time and money out the window when you could be productive.
I think, and I've been around the block long enough to know, you might want to consider a used warrantied unit in better condition from a dealer, put all your money down on it, and 0% the small balance and pay it off early. I can't tell you how maddening it will make you when you wait for parts, have to tear something apart, when you had plans and a timeline.
Now, if you have time to waste when you'd rather be being productive, great. If you don't get excited when you settle for less only to get your wallet and week beat up by the unknowns, great. Keep looking. But, it sounds like you've worked hard to get where you are, and to achieve all your goals. Why settle now? Why buy something just to sell it later. If it's just to do a project and sell it for good and get a push mower, that'll work. But in the long run, with the possible exposure on a cheap tractor without any guaranteed history, you'd be MUCH better paying someone to do it for you with their equipment. Take it with a grain, but I've been there.