Really comes down to what youre trying to accomplish and if you will ever have any assistance from other people (even if its openraid)

If I was starting out, I would definitely have more dual or triple role characters earlier in. So that I can quickly raid with one role and roll on loot as another.

Your love for discipline priest might end soon as well, if leveling is an issue for you I would checkout some notes/videos on healing changes, especially smart heals.

This tool might help plan stuff out for you http://raidcomp.mmo-champion.com/