If you go to purchase extra lynch pins you should be aware they come with different spring tensions. Some are quite easy to flip the bail, some will snap your fingers pretty well if it slips. I would go with the hardest to flip that you can comfortably use. It's really not fun to have a lynch pin come loose and the more spring tension the better.Lets refer to the large pins connected to the implement as "draw pins" and the small clips that retain the arms on the draw pins as "lynch pins."
The implement should have the two lower draw pins installed. They usually do not come with the upper draw pin for the top link, which is not permanently installed like the lower pins are. The implement does not normally come with the lynch pins, but I am sure your dealer would give you the upper top link pin and a set of lynch pins unless they are a poor dealership.
The lower draw pins are indeed usually a different size compared to the top link pin. For Cat 1 the lower draw pins are 7/8" but for the top link you'll want to use a 3/4" pin. I recommend you go to tractor supply and get some extras and keep them handy. I usually have an extra top link pin and some lynch pins in the tractor tool box.