The green sea anemones are cool
Anemones with short tentacles are usually safer to handle and less likely to eat everyone in the tank.
Don't try to remove anemones from rocks because you usually damage their base and they die. I used to carry a hammer and stone chisel when I went collecting. Just cut the piece of rock with the anemones attached and put that in a bucket of water to take home.
If the stuff is from rock pools and tidal zones, it will be fine with a slight change in temperature. As for keeping the water on 55F permanently, you probably don't have to. Monitor the temperature of the water at the beach over the course of a year (including on hot days) and that will tell you how much the water temp fluctuates.