I would say that the brittle star should be nixed just for now. Wait until your tank is established a bit more. If you read any of the posts by ophiura, she has a lot of good advice for stars, and one is they should be introduced a bit later-after 6 months plus.
I like the scarlets better than the blue leg, but that is taste, what about 15 scarlet/15 blue leg so you have more color variety? 50 nass snails still seems like a lot, I'd cut that down to around 30.
I have no experience with cleaner clams, but there is a good thread going on about them now...check it out. I am thinking of getting a couple myself, and I read in the thread you need around 1 per 5 gallons....again, i dont know mch about them.
Emerald crabs I'd get a few more. I really like these guys, they really get into crevices and holes in the LR. FOr a 90 I'd say get 5 for now.
Remember, you are just starting out...part of the fun is adding things, so the slower ya go now, the healthier it wil all be, and it gives you more opportunities to go back and buy more stuff!
Hope this helps a little!