Dynamic, I am going to suggest that you don't get an anemone :(.
Anemone's are fairly delicate organisms and require stable water conditions in order to thrive. A common recommendation is that they should not be added to a tank which has been established for less than 12 months - this ensures that the tank has matured and will be less susceptible to fluctuations in the water parameters, and you will have gained some experience in maintaining the tank and will be in a better position to look after the anemone.
Also, your tank is really too small to keep any anemone with sessile species. It is a recipe for disaster if/when they move in the future (no doubt, while you are away). I think you would have trouble providing the required flow without the waves crashing over the side of the tank and, no matter where the anemone is located, it will never be far from a powerhead - an anemone chewed up by a powerhead is likely to wipe out your entire tank.
Anemone's can live in excess of 100 years in the wild and we should all think carefully before getting one for our tanks.
:)