No three fish can live in an 8 gallon tank, AFAIK. That's overstocked, and in the very least the fish will be crammed and unhappy.
Add at least a pound or two of decent (and expensive) live rock to your set up and let the tank cycle/mature for at least a month. Keep up on the maintenance and monitor your water parameters, and you should be okay with maybe one very small fish. Do lots of research as you go, though.
I started with a 13 gallon tank and have been adding live rock to it bit by bit for a few months. I now have a 4 gallon sump on the tank, 26 lb. of live rock, two occellaris clowns, and quite a few corals.
I'm just starting up a 6 gallon nano which might house a clown goby in the future, or a smaller Mantis Shrimp if I can find one.
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