A 29 gallon tank would be a good starter tank and would provide enough room for a pair of clowns and a BTA. You will want to let the tank become established over a period of at least 6 months before adding the BTA. Perculas often are hosted by BTAs in aquariums, but there are no guarantees. Entacmaea quadricolor is not a natural host anemone for perculas. Do your research for E. quadricolor (bulb tip anemones), they are more demanding than most fish species, but a good starter host anemone species and hardier than the others.