I'm running a team very close to yours - Pally tank, Holy Priest, Destro Lock, Boomkin Druid, and Arcane Mage.
Leveling is VERY easy. Set up simple trash macros that take it easy on mana, and you should be okay. I leveled my team most of the way to 80 with three - the lock, the druid, and the mage, and had no problems outside of instances. The Lock tanked with the Felguard as a Demon spec.
Later on, you'll need to study all of your toon's abilities and weaknesses, and macro with the other toons in mind, in terms of key hit rate (I use a simple one...two...one...two beat and time my macros to it.)
Your casters will be aggro magnets if you're not careful - the mage especially - but with 5 most mobs will die before they reach you (non-Elites). With the AOE potential in your group, you should be able to take out large crowds of mobs.
Study up on /click macros, they almost doubled my dps when I switched to them, Fursphere's thread on them is excellent.
Just know this - the team you're proposing will take a lot more work than a tank/shammy team, as you'll be learning 5 classes at one time, and keep their abilities straight, and then learn how to build their talents, their gear, and their gems/enchants. With that many casters, I would HIGHLY recommend you train a tailor, even your Boomkin will wear +spellcloth over leather gear.
I love my mixed team, as much as it would be nice to have 4 shammies (and I will eventuall), I love teh synergy and utility of 5 different classes, with buff and talents, multiple ressing makes wiping a little easier, I have healthstones and free food and portals...and when the team is running right, they're pretty awesome.