It is best to go Dedicated if you no what you are doing because it is most likely Unmanaged unless you have a high budget.
If you are comfortable to go Dedicated here are your answers:
1. Depending on what your use for it is... if it is high rating forum don't go with a small server, if it is a starting hosting company you could get a Celeron 2.4 which will cover it for a time being
2. Does not make sense
3. You can but each company leads differently...
4. Hard to tell because people post good / bad reviews for the same company so you can never really tell.
5. Being active on the active forums such as Hosting Discussion, and being truthful and loyal to your customers.
6. There are lots, Forum Advertising, Some companies are now doing Newspaper Ads and Commercials, ask customers to reffer people.... but Banner Advertising works all the time
Let me know if you need more information.