Someone familiar with tractor 3 point "in general?"

My rule of thumb is 3-5 threads min, but more the better. If I'm putting the link in compression, I'm fine with 2-3 threads. But in tension I want no less than 3 full turns. I haven't found much good guidance for this either though, but I've used my rules of thumb plenty when pushing and pulling a few thousand pounds of slash, snow, dirt, etc and I've yet to fail the top link or impale myself when working in reverse. I also abuse the ever living hell out of my stuff, its ridiculous. If you knew you were going to put a massive load on the link, I would try for no less than 5 threads..

You can buy different length top links too.
Some top links the ends will come out, others they won't. Tractor supply and North 40 both have a few choices of length in stock. Best to measure what you need, then take your tape with you because the lengths advertised on the links are about as useful as hitch classes.

Class rating of hitches make no sense, it's best ignored completely. 3/4 pins are common, that's what my Ford 3000 3cyl uses. They make sleeves to size up/down, but 3/4 is probably the most common anyway.