Well live rock does play an important role in an aquariums success. Tanks with LR offer hiding places for scared fish, they bring home a piece of there home enviroment so it feels like home. Thus giving the fish more peace of mind and they will punch some natural birght colors with LR too. You could get maybe 50-100lbs of LR in there that would be sufficent.
Now as for the fish the puffer and triggers offten dont work well together, there feeding habbits are very agressive. I think your tank is big enough to avoid that problem, but its questionable. The two triggers will probably be alright, but olny a single trigger is recommended. For the tessolata eel, make sure you live rock structure is very strong, they have been known to topple over LR and kill themselves and tankmates. A way you could avoid this is putt some PVC piping tunnels for the eel to swim through withought disturbing the LR. Good luck!
Evan