Strangely bigger is better.
1st step is read and read next step is make up your mind what your going to keep and what setup your going to do.
With marines the "mixed community of fish I like" is not an option.
nature will quite quickly bite you.
mixing any marine organisms requires an understanding of the inter reactions and living conditions of the organisms.
Having now got over the doom and gloom bit, it is not a black art apply logic and commonsense to your setup follow the basic rules and hey presto it will work.
But then you should have all the knowledge from keeping Freshwater fish under your belt.
Basically if your showing due care to what your doing now by studying, researching and observing before buying, your doing what is right.
Down sides with marines are the parameters can go out of the "Safety zone" very quickly and with some rather sensitive fish and invertebrates it can be very unforgiving.
Along with the perials of buying some very cute and small shrimp that turns out to be members of the order Stomatopoda that will crack the tank as it kill,s your prize Porcelain Crab or the present the wife gets you of that lump of living rock you wanted that is full of god knows what
Up side is your going to observe something fantastic and vibrant. you may get some clowns to spawn never know.
I would go for a basic tank say 4 foot reef get lots of living rock and some good power heads and set up using the Berlin system.
[ame="http://en.wikipedia.org/wiki/Berlin_Method"]Berlin Method - Wikipedia, the free encyclopedia[/ame]
Once mature get the cleanup crew then a pair of peculiar clowns and see how it goes from that point.