I run 20 in the fronts and 15 - 18 in the rear.
For the trailer hook up, try this.
Grab a 2"ID receiver - weld a plate to it. Drill two holes to match the holes in your draw bar. Pop in with bolts. Then use the 2" OD stock for the hitch stock. You can mount the 2" ball on one face an a 1-7/8" ball on another face. (Princess Auto
has pre-manufactured universals in their on-line catalog) Now you have pretty much all you will ever need to tow stuff around the yard.
That is what I am going to do. I already have a drawbar that has been butchered by the PO drilling to different diameters. I finally cut out the extra stock he had welded in (couldn't use me plow as the drawbar was too wide), and now I am touching up the holes, one at a time. Got to practice my welding somehow
Btw, did you get your clutch adjusted?