Depending on the footprint of the tank, I probably wouldn't go with anything smaller than a 10 gallon with two clowns. You can run into territory issues if they feel cramped.
Lighting depends on what you want to do with the tank. What kind of corals do you want to keep? Live rock & sand takes care of most of the 'filtration', but you might consider a protein skimmer. The HOB
ones from AquaC are pretty good.