You'll find my description of how I did my 21' Cal in this thread:Bottom painting a trailerable sailboat
If you're looking for those finer grades of sandpaper you need to look for wet-dry paper. Lowes should have it. It's black. As SailingFool says though, for the bottom paint you're going to want a course grit to etch the hull and give the paint something to adhere to. Use the Interlux 202 before sanding.
Get two quarts of the VC-17 in one color and another in the color you want for the finish coat. That will make your application more uniform and will also allow you to see wear more easily. I didn't do that but wish I had-another lesson learned. (g)
I don't think you're going to find those automobile jack stands of much aid. What might work quite well though is a bottle jack for the lifting and then a couple of 4x4's at bow and stern supported by those concrete blocks. You'll jack each end sequentially until you can get the trailer out from under. Within reason, the higher you get the boat the easier it will be to work on. Read the thread I've posted here and if you have any questions feel free to send me a private message. You CAN do this cheap. (!)
“Scientists are people who build the Brooklyn Bridge and then buy it.”
Wm. F. Buckley, Jr.