questions on sand paper

Hi, newbie here. I have several questions regarding sand paper.
I understand that sand paper can remove the 'orange peel' look on the body of my car(if I m not wrong), so

1. do I need to repaint again after sanding it down to remove 'orange peels'?
2. what the difference between 600, 800 and any other number grit paper??
is it the roughness that makes the difference??
3. where can I get a sand paper?? I don't have credit card so cant purchase
online. Can I buy it in any of the modeling shop??

It will be greatly appreciated if u can spend a few second to answer these questions wif ur professional knowledge.

Thanks!!!

2. what the difference between 600, 800 and any other number grit paper??
is it the roughness that makes the difference??
3. where can I get a sand paper?? I don't have credit card so can purchase
online. Can I buy it in any of the modeling shop??

It will be greatly appreciated if u can spend a few second to answer these questions wif ur professional knowledge.

Thanks!!!

the higher the number, the finer the sandpaper. so 12,000 grit like i have is incredibly smooth (it's for polishing paint) whereas 400 grit is slightly rough.

most tool stores and many hobby stores sell sandpaper, it's alse pretty cheap.

Hallo ;
here some pics to show the difference between paint and sanded with polishing paper
Only Paint witj a little orange peal
http://www.ibk-forum.at/modelle/robert/diverse/lackieren-bericht/zwischenschleifen02.jpg
http://www.ibk-forum.at/modelle/robert/diverse/lackieren-bericht/8000er-12000er.jpg

thsts ,what makes the difference
Greets Lutz