Gear is largely unimportant when boxing.
Five toons in a group, have the firepower that the gear doesn't mean a lot.

If you have the heirlooms, I'd use them.
But it is more important to play classes you enjoy, both the mechanics you'll use leveling and the end result/style of play.
Leveling can seem like a long time, but it's maybe 10% of the game; end level, whether heroics/raids or pvp is the other 90%... and you might as well have something you enjoy when you get there.

You might get to a point, where a given boss is unkillable at your gear level.
But the lower level instances generally are a lot easier to do.

Instances (and quests) are balanced for the 'Lowest Common Denominator'.
Meaning, a group of five random idiots should be able to accomplish the goal.
The game is geared towards and dumbed down to the point where unskilled players can win too.
Everyone can eventually do everything, or close enough.

While you have different challenges, because you're everyone...
You also don't have to deal with an idiot who stand in the puddle of poison, as it kills him.
You don't have to deal with a Healer, whose only move is Holy Nova spam until he runs out of mana, long before the battle ends.
You don't have to deal with a Rogue who only does one move, Fan of Knives.
I've played with single players who do just those two moves.

Playing the entire group intelligently, is generally more than enough to overcome the lack of independent actions.
Not being stupid, or having stupid players with you... that's a huge advantage.




Melee isn't harder than ranged.
It is a different mechanic.
Have CTM enabled, and press (or spam) your IWT Keybind.
Use a slave independent movement keybind to break the movement, if they decide to run off once the mob dies and you're still spamming the IWT.

With ranged, your mechanic is not IWT, it is facing.
You need to run the lead toon through the group, to change their facing.
If you're driving the tank, and you need your toons to turn or do some kind of movement... that's much harder with casters than with melee who are relatively bunched up.

Casters need to watch for spell reflect mechanics, which can easily kill them in the few places where you have that.
Quite frequently a mob can spell lock one of your schools, and in the case of a castsequence macro... that can lock you out of everything for the duration, because the next spell is not available while the school is locked out.
Casters can have mobs who are resistant to their type of damage.

Melee deal with point-blank attacks.
And possibly boss cleave attacks.
Different things to worry about, but not harder... just different.