Want to move SEO optimized website .asp to asp.net

Hi guys

I need suggestion on moving website from .asp to .aspx.But my real concern is my website has more then 200 pages in .asp and well ranked.So

1- Changing .asp to .aspx pages will lose my rankings ?
2- If No,then how to properly redirect my pages ?
3- Which redirect is perfect 301 or 302 ?
4- Can i add each page header with .asp to .aspx redirect code or in .htaccess file ?

Hopefully you understand my whole situation it is big website so don't want to take risk before R & D.

Awaiting for your favorable reply

You should be fine, and a 301 is the best way to go. .htaccess is the easiest/cleanest way to do so.