Yes, i quite agree, it is all confusing...Best thing to do, like i did, was go to your local good book store and get a slack handfull of books on Marine Fish Keeping and read read read...
On keeping FOWLR tanks, the basic things you really need are...
1) Filter ( stay away from undergravel filters...nightmare to keep clean )
2) Heaters ( what ever wattage you need, buy to heaters to make the total....that way, if one fails, the other one will at least keep some heat in the tank )
3) Reverse Osmosis Unit to get the lovely pure water ( we dont want hair algae blossoming in there )
4) Power heads to give you good circulation round the tank so there are no dead spots
5) A UV Steriliser ( my preference, you dont have to have one of these )
6) A good digital thermometer ( stay away from the stick on ones )
7) A calibrated hydrometer, or if you can afford the extra, a refractometer
8) An extra powerhead and heater for your saltwater mixing container
9) Lighting - Deepends on what you are going to keep...or intend to keep in the future..For FOWLR you can use PC lighting, some use T8 lighting, some metal Halide.....For reef tanks, i would always recomend T5
10) Protien Skimmer
12) A very good marine saltwater testing kit
and last of all.....
11) PATIENCE...and lots of
Of course, this is only a basic list...On top of all that, you need your salt, live rock, substrate etc...But i hope it gives you an idea of the equipment your likely to need..
Anybody, if i have missed anything off...please please shout up..
Niko