lobsters (aka. crayfish) do not work with plant tanks... or even most fish only (FO) tanks. They will act like bulldozers to your plants, and will try to eat any fish that get within their grasps.. a good species only type animal, not good for community tanks.
Clown loaches will work fine in a plant tank, but a 75 gallon has a limited foot print. Clown loaches normally get around 8-9 inches fully grown in captive, but can reach sizes of 12 inches. A 75 gallon has a footprint of about 48"x18" correct? 5 would be a bit much... I'd probably go with 3.
For schooling fish... how large do you want them to be? Personally, I would love to see a planted tank with 50+ fully grown cardinals in it.
HTH
-Richer