Not a problem at all. They are not different protocols. zwave plus just adds a few command classes and has different power management and signal strength.
Yes, the easiest/official way is to make a backup and then restore that old backup on the new unit.
Yes likewise. The backup/restore should work.
No, Unfortunately. It hasn’t gotten any better. For one the video streaming through the vera is poor and it shouldn’t be used for it. It just doesn’t have the horsepower to do it. You should use a dedicated NVR for it. As for control of PTZ, there are plugins which can do it. I use one for amcrest cameras but can’t rely on it for anything else.