How much life can I sustain????

[mozart200]

I have a 75
fluval 404
emperor 400
prizm skimmer
about 20 pounds of LR (planning on getting more)
I am hitting it with 210 watts at this time (compact flourescents)
critters
misc. crabs, reds and blues
emerald crab
snails
gobie
yellow tang
blue tang
3 clowns
1 anemone
1 mushroom
1 star polyp

 

[bang guy]

You can sustain quite a bit more life in there. However, if you want it to thrive and do well you're almost at your fish limit. IMO having 3 clowns isn't a good idea.
You could add a LOT more mushrooms and polyps to fill in the bare areas once you get more rock. A centerpiece LPS like a Frogspawn or Open brain would also be a good fit.