I'd say 3 or 4" wide would be good for the snowflake. Do a search on wetwebmedia.com and see how big in diameter for sure.
Shark, lionfish and snowflake eel should generally be alright. Shark and a bluespot(assuming a ray?) need a ton of ground space and not much rock, esp the ray. Be sure to use fine sand as well. A wider instead of taller tank is better for both the shark and ray. If you could make it wider instead, that would be better.
I might be concerned about the lobster, ray, shark combo. Even if the ray/shark aren't big enough to take a shot at the lobster will the lobster pick on them since they are bottom dwellers? You could try it and see how it goes.
Garden eels need a deep sand bed and shouldn't be housed with fishes like these.