Pro Sites & Domain Mapping plugins

A few questions:

1) I would assume a dedicated IP is required for these plugins to work correctly? Will they function in a shared hosting environment or will they require a VPS / dedicated server?

2) How is the domain mapping handled? It’s registered then gets pointed to my server IP?

3) After a domain is mapped, is there a way to specify MX records for the domain to allow for email hosting?

4) Do these plugins allow for a unique userbase on each hosted site? ie. I don’t want users of siteA.com to be able to log into siteB.com as well.

Thank you in advance!

Best regards