I have a dedicated server I purchased to host multiple VPSs, including one for shared hosting. The shared hosting VPS has access to 4 of the 8 cores, 4GB of RAM, and 750GB of hard disk space. It has support for a plethora of languages. This will be a multi-resolution to one IP. My questions are:

Should I charge per-client, or per-site?
What are the recommended packages? 128MB of ram, 20GB storage?
Is there anything I should know about shared hosting?
Where can I go to advertise?