You'll get him. It sounds like you are on the right track.
About him being super annoying, we thought the same thing when we first starting working on him in heroic. Since getting that first kill though we've had no trouble at all farming him - and I suspect you guys won't have any trouble doing so either. Once you work out the CDs and people minimize the damage they take from firelines, this kill should be in the bag and on farm for you guys. The only other thing you may need to improve is slowing the slimes a little more - that could make the difference for a kill (a frost dk using HB on them when there gets to be a lot works great).