If the cleric goes laser and as controlly as he can, I think your own real concern is not to throw too many brutes at them at once, cause without the defender to go toe-to-toe with them they'll take some people down.
If the cleric doesn't do that, you also potentially have a problem with...
This caused a neat moment when I ran it where the party's Paladin/Fighter managed to Tide of Iron the Wyrmpriest off the edge off of his platform, whom then proceeded to get smashed by the boulder before he could get out of the way.
The specific 4th edition rules abstractions tend to move you a little more towards an authorial stance and a little away from an actor's stance, where the decisions you make are the decisions your character makes.
That seems to be the main point of resistance to this sort of thing: it requires...
Concern
I think the xp rules oughtta do it by themselves, assuming the players know about them.
The only thing I'd worry about is that if they are very successful at taking on multiple encounters per day, which your momentum system will help them with, then they're going to level up faster...
It seemed obviously required to be within melee weapon range of the warlord to me, but I won't get into any argument about it.
The weird implication of this to me is that I think half-elf Warlocks will always want to carry around reach weapons they aren't really proficient in. Cause this seems...
First encounter of the day is 80% xp, second is 100%, anything after is 120%? Numbers might need rejiggering, but I'd imagine something like that, while being a little bit of a sledgehammer, might encourage the players towards bravery without derailing them totally if they opt for caution.
Just starting something out. It'd be relatively simple at first, cause everyone is just learning the rules.
Even if you can't commit, please get in touch. I've moved back here after being away for a long time and I don't have the nerd contacts I once had.
We've got a few players already...