CC, you are at least starting out better than I did. All I could find were cheap 80 grit belts at first. How sharp does a machete need to be? I thought I was the only one fanatical enough to strop a shaving edge on a machete, and then go beat it up. Used my machete all yesterday afternoon on some wild wax myrtles. I am assuming you have one of those cheap 1" x 30" sanders, like mine.

1. If you are going to use the sander for sharpening only, I'd remove the adjustable stand or rest, too. This will give you more length of belt to use and allow placing the edge in the center area between the two wheels for a great convex edge.
2. I have used polishing compounds very little. Cold One knows more about that stuff. Just stroping in the leather seems to work for me. Look at the edge frequently to see just how and where you are hitting the edge. I have had best results using VERY light pressure as my belt is a bit loose.
3. Since I have never measured an edge angle in my life, all I can say is keep practicing and experimenting and see what works for you.
4. Ontarios are "expensive" machetes. Get some cheap $6.00 Tramontinas from SMKW. Not only are they cheaper to practice on, they are great machetes.
5. Wear eye protection and be careful. Have fun with it. The more you do it, the more you will develop a technique and feel for which sharpening angles work best. At first, try to approximate the factory angles as best you can.
Hope this helps.