Rudy,
Wish I could help you decide how much flow you need. I've experimented with various sizes of Hagen 301s, 402s and 802s in our two tanks with anemones. Whatever powerheads or filtration systems you choose, they
have to be bullet-proof in not sucking up anemones that move around your tank. When you are experimenting, anemomes are very likely to move, too
Here's the
Wavemakers, Powerheads, Heaters section from the new
Reference Library for you to do some research ....
http://www.canreef.com/vbulletin/showthread.php?t=22049