Hi Dale,
You can definitely upgrade to a VPS from your current reseller plan. You will be able to use private nameservers even on a VPS. Each VPS includes 2 dedicated IP addresses, which can be used to setup private nameservers.
RVSitebuilder is available as an addon with VPS and Dedicated Servers.
Fantastico comes within cPanel control panel. You can check the scripts included within Fantastico at
netenberg.com || creating possibilities
Fantastico is a 3rd party product and we don't have direct control over its features and functionality. Fantastico is constantly updated with new scripts and applications while older ones are being removed.
Please feel free to post if you have any more questions.