Welcome to the forum.
If you do a search, I'm sure you will fine all kinds of tips. If you can't find any advice out of 21000+ posts, you might have a problem.
As far as if you have to sand through the original clearcoat...is there any other info you can give.
Is the clearcoat bad?
Are the pinstripes on top or under the clear (traditional type stripes or retro type aftermarket stripes)?
What do you mean by "sand through"? Do you mean strip the clear off? Or, just...sand through?
Is it the original paint you want to sand through?
When you say 'primer' do you mean sealer or primer. you said primer, but as far as I know, there is no white primer.