There are a lot of things to consider. If this is your first 5box group and you don't have any or much boxing experience, I would keep it simple. Paladin tank and 4x whatever. However once you get the basics and some advanced stuff down, you will prolly enjoy a mixed group better. Take a minute and think about the group you want to put together and why. Here is some food for thought.

Here are some things to take into account when makeing a group.
Who can heal?
Who can rez?
What armor do they use so drops don't go to waste and your not having to farm something 99 times to get 4-5 of the same drop.
What buffs/debuffs do you have? Things that lower your hit cap, Boost your crits, MP5, spell power etc.

My mixed group that I am going with is a Paladin, Druid, Priest and 2x Shaman.
All can heal.
All Can rez.
I can use all armor drops, only the two shaman compete for gear.
Lots of buffs, totems, debuffs
All can AOE,
All can single target burst.