I am used to played 1 holy priest, 3 ret pallys, and 1 prot paladin. I am wanting to try to a mixed class like for example:

Prot Pally
Holy Priest
1 or 2 Mage
1 or 2 Warlock

I was wondering if anyone had experience in mixed classes, if this combo would work? Also if it doesn't any recommendations on what classes? Lastly how hard of a transition do you think it will be from my current group into a mixed class as shown. I mostly just do pve, no pvp if that helps.