2 chains at 4700 WLL (working load limit) makes for 9400 combined WLL. Far more than is required for the weight. I'd get 4 of the 5/16 grade 70 (and make sure they are stamped with the grade, probably either "70" or "G7"). Last time I got some I painted a couple of the stamped links on each one.
I'd get a couple 14s and a couple 20s. If you decide the 20s are too long, depending on how long of a chain you need, you can cut them down and have more shorter chains. Just make sure any replacement clevises you put on them are also rated grade 70. 5/16 chains are a lot easier to deal with than 3/8 because of the weight, then there's the added cost. One 3/8 G70 chain also has more WLL than legally required to hold your tractor, so it's overkill.
5/16 chain uses the same binders as 3/8. I prefer lever binders, some prefer ratchet binders. The ratchet ones work good, but you have to keep them very well lubricated. And where I am, that would mean oiling them every time you got them out.