I am also doing similar
paladin tank
paladin heals
mage x2
warlock

I made a test group in bfa and have been leveling them up to ge1 the general feel of running this type of combo. I think they are level 17 now. i feel by doing this i have already learned alot for going into classic with this team. spells and leveling speed will be a little different but the overall feel i think is similar enough to know if i like how the mechanics are going to work.