I'm currently on my eighth or ninth finishing project. On some of those bodies I experimented several times over them. Very work intensive in all cases.
I've seen cars being painted. Believe me, compared to cars, painting guitars can easily be much more work intensive if you want something resembling professional-level quality.
One thing I can guarantee, though. Nobody achieves good results on their first shot at refinishing a guitar.
1. How would you know kung maganda preparation ng body? And how do you prepare it?
Sort of what they said. Sand it down. But in many cases, stripping to bare wood isn't necessary. Keeping the sealer coat flat and intact will suffice, unless you're going for an oil finish or something. I'd advise against using a power sander, unless you're adept at handling one. Those things will sand through both paint and wood hard and fast.
2. What kind of paint?
Acrylic lacquer, nitrocellulose lacquer, enamel, polyurethane, polyester, varnish, oil, etc.... take your pick.
3. Whats a top coat?
What they said... clear coat.
4. What is "wetsanding"?
What they said as well: sanding with soaking wet paper, or even oil, depending on the finish to be sanded. Some people also mix oil-free soap with the water for even smoother sanding.