HAHA you will regret doing it by hand after 5 minutes that's for sure. Orbital sanders are great but like the saying goes you get what you pay for.
IMO your better off buying a "cheap" 5" grinder over an orbital sander. There are plenty of good DIY and tutorials that covers the basics for bodywork so have a search on google.
The best piece of advice I can give you is make sure you wear your protective equipment and dont get carried away eg: if you start on the frh guard finish that before moving to another area.
Oh and make sure you take plenty of pics along the way