1. No, not if you like the Barbarian. Regen is really nice, but you have to look at either a Troll or Iksar for 60 levels. Not a bad thing, but do you want to?
2. If you want to tank things stack hp's. Strength will have minimal impact on your damage output. PWC is good but if you can afford it, the Barbarian Spiritist's Hammer is amazing. I've been testing it and from 30 up until whenever, it seems more of a thing for leveling to me than either regen or frontal stun immunity (procing at least once a fight for me).
3. Not really been to velious yet.
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4. I think the only change is that all epics now have a level requirement for equipping?