That's kind of the reason why I'm afraid of using sandpaper (that it might cause scratches to the model) Is there a particular type/method of sandpaper to avoid the scratches?

Where can sandpaper with grit that high be purchased? And how much do they cost on average?

Ok. So sand the thick top coated model while gradually increasing the grit of the sand paper. How many layers of top coat is considered thick? And how many cans of top coat is likely to be needed(not sure about you guys, but I intend to paint and polish each individual piece before assembling, with the exception of the internal skeleton)?

Model in question: MG Strike Freedom(I know most ppl use flat top coat for their gundams, but I want to try and make mine shine ).

Regarding the sandpaper, those types of grit(600,1000,1500,2000) can be found from art shops or from hardware stores? Anyone have a specific recommendation of grits to use on a model?