If you're actively trading for these cards, you absolutely want to get the gravelocks (and gravehawks, if you can manage) first. Gravelocks are all about numbers. The more Gravelock Elders you have on the field, the more powerful each invidual gravelock will be. And the more gravelocks you have, the more beneficial the buffs from gravelock elders will be. Gravehawks are just icing, gaining strength for each gravelock and gravelock elder on the field.
If you can't amass a giant ball of gravelocks yet, you'll need to suppliment with other units. Sisters of the Fox make good cannon fodder, since they net you a free draw card, and you won't be using your growth resources most turns anyway, so there's no reason not to put them out there. With stats of 1/2/1 they're really only going to act as poor meat shields though, so you may decide against it. If you like using the lobbers, golem skin may be a worthwhile buff. Eventually they get in the way, and golem skin will destroy all structures on your side to increase the attack/health of one unit by 1 for each structure. If you're using hellspitter mortars though, you may not want to use this unless they're about to die, as they're too valuable to sacrifice for a buff. Golem skin can also make use of the various memorials you'll be putting out, as they really serve no purpose once they're placed, they don't have to survive for you to keep the resources they provide. The enemy will usually kill them off quickly anyway, though. You could consider adding in rigging, to make those memorials do damage when the enemy destroys them.
Avoid the temptation to use golem skin on a big bad like an Iron Golem or a Cannon Automaton. This might make you feel awesome by having a walking death behemoth on your side, but you'll feel pretty dumb once they use a violent dispersal to instakill it, a pushback to undo its buffs and send it back to your hand, or a root to make it unable to move.