Have never done it but from what I have read over the years my biggest advise is absolutely no power heads in the tank. Accomplish your flows using external pumps, provide sufficient intakes using 6" screens so the anemone does not get stuck. It is disheartening the number of times I have read of anemones getting sucked up/and or shredded by power heads. I personally would use 4 sea swirls on this tank, which may be a game changer if you are going open top.
I am sure I will get some "I can do it" responses, and that is fine, but many anemones generally come from shallow grassy areas and other shallow sandy lagoon areas and will probably benefit more from metal halide lighting than LED lighting. Full disclaimer in that this is my speculation and not experience. But if I were setting this tank up, they are one of the few animals that I think would still do better under MH. A single pendant fixture would be good.
The Atlantis Marine World has dedicated clownfish and anemone reef tank setup back in 2000. I don't know if it is still up and running, but it is worth checking out their specs.
Not too many people do anemones because they don't really mix well with corals (again, cue the I can do it crowd here) but when done correctly, they are very striking! ...and I think better than a SPS tank.
Any particular clowns in mind? IMO, a pair of any type will be better than a collection of different types. Being a 30 gallon cube will limit you a little but you still have a few options.