First I'd just like to say Welcome to OpelGT.com. This site has some of the nicest helpful members you can find. Start off by just browsing the forums, and get used to using the
search button. Most of the questions you have, have probably been answered once or twice before.
Some parts are hard to find in good shape, but many are readily available new and used. If any body panels are needed, your going to have to do some searching. Many members just fix the rotted out spots with new sheet metal and finish it off with a little body filler. The only source to new panels would be ordering over-sea's, and those aren't cheap. There is also the
classifieds section, where you can buy, sell or trade parts and cars.
eBay can also be very useful to find parts. Make sure the seller has more than a couple feedback and make sure their mainly positive.
Like I said earlier, that search button is going to be your best friend for a while. Going over the forums will tell you pretty much everything there is to know about Opels.
Here are some links to get you started:
Things You Should Know
OpelClub.com - Facts
The Definitive Opel GT Guide
Posting and You
Opel Association of North America
Service Manuals
Common Rust Locations
Visual Opel
Restoration Costs
Cars and Parts:
USA Opel
Opel GT Source
Opels Unlimited
Lenk Tuning International
Suselbeek
eBay/Craigslist