they are tiny, the biggist I've ever seen are only 3/4 of an inch, and that is a huge one. the other things about them are as follows, they are very territorial, in my 24 I tried to keep 2 pr and the older pr killed the new pr over night. The are also very nocternal, I don't see mine during the day and I've had them over a year. I see them occasionally at night with the moon lights on, they seem easy, I feed them pellets and frozen. The books say they eat starfish and urchin tube feet, but I have never had them bother any of my stars, and in the ocean I've never seen them with a star or urchin, but that may be just because they are easier for me to find when they are not feeding.
My opinion is they are very cool nad interesting, but you have to be careful, they are not good display animals as they don't come out when the lights are on, and they are tiny so you have to be careful not to put them with things that could eat them, in your tank they may not be the best as I think your wrasses will eat them, although I have a pr of leopard wrasse with mine and they are under the sand so they never see mine, but if they find them I have no doubt they would eat them.
Good luck, I love mine, just with they were out when I'm awake, but I knwo they are there.