Definately my favourite fish, soooo much personality and they 'put their pyjamas on" at night which is too cute (you have to see it to know what it means ). Mine is about 3" long and is in a 20g with a tiny Coral Beauty (yeah I know the tank will be too small for it eventually, it was a present long story) and a Sixline Wrasse. He gets on great with both fish. They are a very peaceful fish but can defend themselves fairly aggressively if they need to. Also a good fish to have for algae control. I'd say a 20g is the minimum for one, and they are good jumpers.
I have seen a couple of Bicolors over 6" long but that was only in really large tanks, in smaller tanks they seem to stay around 3" to 4".
I agree. They are wonderful fish. They might hide the first month, but soon they will become more bold and swim around looking for algae.
And they fit in nicely with a community tank. They don't bother the shy fish (like my bangaii), but they will stand up for themselves when a bully (like my clown fish) tries to push them around.