Since you are just starting off with real RC, do not get a nitro RC to start with. I have ran RC's for 12 years, and anyone else that has run RC's half the time I have can tell you start with electric.
1. This is exactly where you want to be.
2. You can run trucks on road, but they arent as fast. The trucks have different drivetrains and suspension. If you want to do ramps, get a rally truck. If you want to just race on dirt, look at a rally car (some can me tricky to find).
3. Tamiya, HPI, Schumacher, Team Associated, Team Losi, Traxxas, are some that I can think of off the top of my head.
4. Electric and Nitro can go the same speed, it just depends on your set up. After several modifications, I can hit 50-60MPH with my Schumacher on road set up.
5. Lots of maintence, disassembly, reassembly, so on and so forth. Should be performed after every run.
6. Depends, if you put a cardboard ramp there, you're fine with anything.
7.
www.towerhobbies.com,
www.hpi.com,
www.racingcars.com,
www.stormerhobbies.com,
www.tamiya.com,
www.google.com, as well as your local hobby shop.
8. Do not get a nitro to start with. I have run nitros, I have run electrics. Nitro's are just a noisy pain in the ass. In all my 12 years of RC, I have owned 15+ Electrics, one nitro that I got rid of about 2 months after recieving it.
9. A good RC, RTR (Ready To Run), costs about $150-$300. Kits are less expensive, but then you spend $150 on electronics so it can run.
Hope that helped! Feel free to ask more questions.