The size of PVC is like just over an inch. so you could make a box and have 5 pvc pipes. drill through the bottom up to the pvc. you dont want any bumps on the top of your rail. you can attach the pvc together. thats not a problem. and i dont no how tall you are. build as high as it can be until you can sac yourself. so a bit higher than your knees
1) 3 or 4 1.5" tubes, there's no real performance difference but 4 looks nice and is better for snowboarders.
2) A works just fine and holds it nice and sturdy.
3) You're going to want to wedge a thin piece of wood under the end of the uphill PVC so it raises it above the downhill one, make sure you raise it enough.
4) Anything between 8 and 12 inches should be about right, 6 inches if you wanna use it solely for learning new dances.
2. "A" works well, It holds the pipe really sturdy as stated^. A common question is "Will it still slide well, or will I get caught up in the holes?" And the answer is It slides perfectly. The bumps do not affect you at all.
3. You do not need to raise up one end of the pipes. Just stick the next pipe right after the last pipe. What I did, I just made it so that the pipes have the seams at different places in the rail. So not all 4 pipes seam at one point.
Check out my rail, I think it's pretty similar to what you are making, only 14' long instead of 20'.
around $30, but I had some of the wood already