From experience I don't find energy grenade launchers all that great on a full energy build.
They are heavy and there's little use reducing enemies resistance on an energy mech. The extra damage you get for depleting the enemy mechs energy covers the extra damage you need. Much better to have a heavy energy depleting weapon like a deep drainer. You ideally want to get the enemy mechs energy as low as possible, as quickly as possible then combo them with teleport/hook and call of lightning for huge damage.
There are problems with energy mechs though. Due to the popularity of kits and regen modules, it's difficult to get top players energy down to 0 and the added resistance will really mess up your damage. You won't be able to finish a fight quickly, which is the aim of an energy mech.
As for your modules, try your own things out and see what works for you. Ideally you want to fight a heat mech to see if you can keep piling the damage on when they try overheat you. If you can then don't worry about heat. Then work on your energy. You want to try fight an energy mech, but don't beat them comfortably. You need to outsmart them, so you deplete their energy before they get yours. There's a lot of cases where I've faced an enemy energy mech with more regen, but because I've depleted them first I've come out on top. Just takes practice. For me on a spider build it took 2 cd/regen and an energy module.
I haven't played energy builds in a while though, as they are easy countered now that kits have no weight
