I recommend sticking to a mobile playstyle in this fight; run between his legs if he's on you, keep moving to avoid the worst of his attacks, time your big cast and channelled heals to when he's obviously targetting someone else. To be honest, I do find it a lot easier to heal on my scoundrel than my sorcerer because of the scoundrel's instant-cast heals and HOTs.
This isn't a good idea, he'll just turn around and sweep everyone who was properly positioned behind him. It's particularly bad after his smash and will get someone killed.
When someone is targeted by Bonethrasher they need to stop in their tracks and take it, while the rest of the group continues to reposition behind him. This is one fight where Guardian tanks can use Guardian Leap every time it's on cooldown (when they don't have agro) without any risk, and it will help out your healers some.