I wouldnt put the anemone in a 5.5...and plumbing it to your main tank just makes it that much more of a problem if the anemone goes nuclear. I agree with the min for an anemone being a little higher...maybe a 10g would be alright. A 70watt halide would work great for that.
IMO, Clownfish are the goldfish of the sea. Unless you have a large tank with a large enough anemone and other fish...you never really see their natural habits. In fact, some clownfish become too nasty in smaller tanks anyways, and w/o enough space, they never show their natural bahaviors anyways. They just swim in the corner like a blind goldfish. I find them to be the least personable of any reef fish.
I would put the anemone in the 55g and have the 5.5-10g for some other unique critters.
Mantis shrimp, Pistol &
watchman goby, Jawfish, Seahorses, Angler, breeding pairs of shrimp, neon gobies, etc. All much more interesting and easier to maintain.