My entrance to massacre was squire with dragon. Push and gear up act1 then act2. Easiest done in group doing act 1 and 2 most people will be similar gear (except alch lab with people farming weapon) Build a decent hunter. For building. Traps and aura are the only things to build on most maps with barrier. Then either go hunter with cat or monk with genie dps. Either way need couple thousand health and dont forget to upgrade armour to cap. Apprentice is of no use currently.
my general rule of thumb and i may be wrong :) is priority list : up grade if available 1. number of projectiles 2. Rate of fire 3. regular range damage. Regular range damage is boosted by hero attack stat but elemental damage isn't.