Cat2, there are numerous good threads on grease selection if you use the search feature.
Problem of mixing incompatible greases is that the resulting mix may be either too thick or too thin to work right. This problem is largely solved by more frequent greasing when you switch, to flush out the old grease.
If both greases are the same base, such as lithium complex, there should be no issue. FWIW a great many common greases are lithium complex.
Moly or no moly is your choice. Moly is generally highly recommended for areas that get large impacts, like loader pivot pins. I'm not aware of high speed problems for moly that Snowridge alluded to, and in fact I have a can of wheel bearing grease (for on-highway wheel bearings) that is heavily moly fortified. If there are high speed issues I'm sure it's at a much higher speed than any greased part on a tractor operates at.
I personally use JD brand grease because it's easy to find, low cost, I can actually find its specs on JD website, and I trust JD. However I would imagine that most if not all greases sold in reputable stores would work fine, as long as you buy one that is labeled for your type of use. Meaning, buy a heavy duty type grease, with or without moly, avoid the greases that are specifically marked as light duty.