I have to say I am impressed that a Defy XT is still operating!, (my first smartphone) .
1). Yes. transferring from the RW Moto 2nd Gen. to the 4th Gen. is likely routine.
2). Yes. this should not be a problem, but RW support is quite competent if required.
You should note that both users plans will change. The Defy Plan? will have to move to 2.0 (your current plan?), and the 2.0 phone line will move to the 3.0 plan.
I hope that makes sense but, the bottom line is Yes, it is not that uncommon.
I would suggest using this thread to help walk you through the process if needed, and ask your fellow community members(us) for advise if uncertain.