Hi, here are some answers/comments:
1. Yes - it is NDU and the DM is used to do it. There is a section in the Deployment Manager guide that talks about this process.
2. 4.4 is the latest RP code and I would suggest it given some of the enhancements with XtremIO, but 4.1 SP2 is technically supported with XtremIO as well.
3. Check out the RP Deployment with XtremIO TechNotes - this will explain the integration, which is essentially adding the array in the array management section and giving it the user/passwd to the XMS IP.
4. If VNX is the target and you plan utilize continuous snapshots then it will stay the same in terms of the sizing like you have above with the 20% RoT. The replica will have to be the same size as the source.