First off, I asked this is the ultimate refinishing theme but nobody has tried to answer it.

I'm clearing my guitar with Minwax fast drying oil based polyurethane. I know that stuff sucks, but I'm a college kid on a budget and I gotta go with what I can afford. My question is simply how many coats do I need to apply so I won't sand through the finish it when I polish it in about a month? I've got 8 coats on now top and bottom, and the grain and cracks and everything is almost completely filled. I was going to go to 15, but I've read about people brushing on polyurethane and going up to 20 coats. Do I need to apply that many coats? I'm thinking that I will need to do more than I originally planned because I'm sanding in between coats, 220 for the first 2 or 3, then 320 for the next 4 or 5, and now I've moved up to 400 grit. I just want some thoughts and advice from the paint gurus here.

Thanks in advance.
1998 PRS CE 22-10 Top Natural Finish
MIM HSS Strat-Electron Blue
Speaking from my personal experience using those sprays, it really depends on how much you're trying to smooth it out with the poly - if your base was really smooth to begin with, and you're not trying to poly over surface imperfections, then you don't need to go overboard. I usually polish with rubbing compound then polishing compound by hand, and 15 coats is more than I usually do on anything.

On the other hand, if you're trying fill in grain and cracks, you could be in for the long haul.. ideally you would have used a filler of some type to even out the surface before you did the poly.