To answer some of your questions. The aggression issue yes the clowns will aggressive to both members of their own species and to other fish that get to close to their anemone. The level of aggression depends on a couple of issues like tank size, tank mates and most importantly the type of clown you want to keep Maroon and tomato clowns being somewhere near the top of the attitude list and perculas and occelaris clowns being near the bottom.
There are several ways to mitigate the clown aggression issue. Try to get to young clowns out of the same batch they will work out who's going to be a girl and who is going to be a boy with a great deal less fighting than with two strangers. As to their lever of aggression to other fish ," again this all depends on what sort of clown you're after" there are a couple of things that you can do. If you want to get an aggressive species like the tomato for instance I'd add it or them after all other live stock was place in the tank including their anemone. This will usually work unless the anemone has decided to locate in someone else's territory," not to common since they eat fish." This will give your shyer inhabitants a chance to get themselves established before the clowns come to town.
I'd also try to make sure that the anemone is significantly larger than the clown fish. I've seen all too often cases of an anemone loved to death by it's clowns. Especially the more aggressive species. I'd also give the anemone a month or so to adjust to the tank and to find a place to settle in.
As too the hawk well lets put it this way I'd trust it with a cleaner shrimp about as far as I can throw a 500 gallon tank full of live rock. I'm not sure what else to recommend to you there are a lot of different choice out there! I know how frustrating it is to want a critter only to find out that you're going to have a nasty in tank situation if you get it

. Trust me frustration is much better than trying to make it work.
As to the carbon it depends on what you want to keep in your tank. I'm in the minority on this board I only run the carbon if my water is cloudy, one of my critters starts looking droopy or in other unusual situations most of the folks here run it 24/7.
hth welcome to the wonderful world of salt water the surgeon general warn that you may become addicted with the purchase of you first fish.... Oh well probably too late for all that.

Chris
p.s. If you're doing this right you never stop asking newbie question :dance