I'll also say Nix the cannister filter idea. I would run a HOB protein skimmer and a HOB filter (like this one but whatever size you need
http://www.jlaquatics.com/product/pf...er+Filter.html) full of LR rubble, you could also put carbon and phosphate remover in it as well.
Nitrates are fine in FW but in SW they can negatively affect your corals. FW fish and plants just don't care about nitrates, corals do.
As for flow, the best way to get it really does depend on your budget. If price were not an issue I would go with a vortech MP20. If like most of us you're on a budget, a pair of Koralia 4's would be a good place to start.
As for the heater, I would personally go with 2 smaller ones. That way if one sticks on, it's not enough to cook the tank by itself.
Good luck and don't be afraid to ask questions!