1: you can use real ocean water, it might smell alittle too much but you can use it. You should still treat the water with elements, and a marine ph buffer to raise the ph to 8.3. Personally it is a fear of mines to use this, as make it yourself saltwater isnt hat hard or expensive, and the ocean might have other things you dont want growing in your tank.
2: Saltwater will get expensive, your going to need live sand, which is around 1 pound per gallon and live rock which is around 2 pounds per gallon. Then i would suggest since you are using real ocean water and this is a semi large aquarum, get a protein skimmer. You will need a good filter system, hydrometer to measure the salinity, water treatment like elements, buffer,
lighting is awhole different issue, corals need high lighting, so if you plan on making this aquarum reef, you will need a stromg PC lighting, T5 or metal halide which is easily over 400 dollars.
3: slatwater tanks dont need that much work, but certainly more than a freshwater aquarium. You have to check water chemistry about everyday and compisate for any changes. The cleaning also requires more time.
I put well over 2 hours a day into my aquariums.
