Rainbow Urchin and other new additions

[ms. fish]

Anyone think that putting a rainbow urchin in a 28 gal is a bad idea? The tank finished cycling in October, but I've been taking it VERY slow. I have the following so far:
6 blue leg crabs
6 turbos snails
6 bumblebee snails
1 emerald crab
1 porcelin crab
1 flame scallop
small colony of yellow polyps
clove polyps which were hitchhikers on a rock I bought
I'd love to add the following:
1 Rainbow Urchin
1 Boxing Crab
1 Sally Lightfoot
1 Hawaiian Strawberry
Anything I should think twice about on this list?

 

[ms. fish]

Oh, I forgot. I want to add percs too, eventually. What kind of anenome do percs like, other than carpets? I have a nasty carpet in my 90 and I'd like to stay away from them in my reef.

 

[harlequin]

The rainbows are not reefsafe like the tuxedo urchins. Everything I have seen on them says they will eat soft corals. If I were you, go for a Royal(tuxedo) urchin which look similar but have blue velvety stripes and are completely reef safe, they dont even knock over loose rock. They also look really cool and not real(for months my roomates gf swore it was fake) .
I would hold off for awhile on the anemone. They need extremely good and stable water conditions. They also need good lighting but I assume you knew and have that already. I wouldnt get an anemone any sooner than 6 months after cycle if not more.
I think a boxer crab might cause problems with your other coral too since it has a pair of stinging corals on its claws and could bump into them. Other than that I like the list.