a pair of ocellaris clowns will pretty much fill that tank - they are some of the smallest clowns but still get to be 2-3", and if they actually pair up they will claim most of the tank as their territory. you might be able to fit 1-2 more fish in, such as a lawnmower blenny,a chromis/damsel, dottyback, goby or small tough fish such as them that will eat prepared foods.
for corals, if your main focus is a pair of clowns and an anemone i would stick to the easy/hardy soft corals, such as colt/kenya, mushroms, xenia/anthilia, and zoanthids/palythoas. and a few invertebrates such as blue legged hermits, brittle stars, snails etc. there is enough variety there to make a beautiful tank that wont drive you crazy trying to keep all the parameters in line. the anemone will be your biggest problem, as they can be very picky about water parameters.