Let's look over your list.
75 Gallon Tank - Bigger is always better in saltwater. You have more chance to notice bad things since they happen more slowly or not at all due to dilution by the greater water volume and its added stability.
Lights( Regular Flo) - This will not have the moonlight feature of a marine lighting system, something not only a benefit to the aquarist who can see the tank in a transformed personality this way, but it also greatly benefits the animals in the tank, providing a more natural environment. Regular tube lights will not provide the light spectrum to see the colors of your fish at their best, and the fish will begin losing color without proper spectrum lighting.
Filter (probably a canister) - Very 1970! Canisters did work then since there was only one better system at the time, but you had to accept a gradual loss of vitality and the eventual death of more delicate marine fish. A sump with live rock and optionally a refugium with a live sand bed and Chaetomorpha would be much better. The sump and refugium can have an opposite day/night cycle to the display tank, which minimizes the pH drop when the lights go out. Some kinds of marine fish need that refugium because of the zooplankton that reproduces in the live sand and Chaetomorpha plants, and is washed into the display tank to provide a natural food containing substances we can't provide with prepared and frozen foods.
Protein Skimmer - Essential! Pick one that is rated high. Reef Central is a good place to find discussions on this topic.
UV sterilizer - a nice option for a hospital or quarantine tank, but not useful on a display tank.
Aquarium Salt - highly overrated in freshwater aquariums, and absolute Death in a marine tank. Use a quality artificial saltwater mix such as Reef Crystals or Instant Ocean. A RO/DI unit will provide more suitable water for mixing than tap water.
Hydrometer - A refractometer is more accurate and more dependable, but you can use a hydrometer with a little practice and care and learn how to get a higher percentage of good readings from it.
Test Kits - A TDS meter, and other test kits or devices as needed. Or if you belong to some reef/marine aquarium clubs, the club may own some of the more costly testing equipment exclusively for members, making membership in a club near you well worth the dues.
Live Sand - Because live sand can go bad, it should always be in a refugium that can be isolated from the main tank and sump, never in the aquarium except as a thin decorative layer.
Powerhead(s)? - Water movers are essential, but powerheads are a high waste heat source and high energy method to accomplish this. Hydor Koralia water movers and a controller use a small fraction of the electricity powerheads do. I have switched over almost all of my powerheads for the water movers.
Mixing bucket - Essential. this is where you can use one of those powerheads still if you already have them. Aeration does not provide complete circulation, leaving dead spots, and it causes a salt spray that can damage anything near the mixing bucket. A great mixing bucket is a replacement salt tank for a large water softener. They have a nice fitting lid and a floor space saving shape. They look nicer than a new Rubbermaid garbage can but do cost more, unless you luck out.
Net - You will need two or three sizes. Also a fish trap since some marine fish are nearly impossible to catch with a net without first removing every bit of coral and decor in the tank. Don't put the captured fish in the mixing bucket. Have at least one isolation tank, probably more.
Additives - A calcium reactor will be much more effective than a buffer in keeping pH and calcium content of the water high. Live rock and aragonite sand or gravel can help protect against massive pH drops. Kalkwasser is a good product to maintain alkalinity (pH) and calcium, is simple to use, and has some side benefits in discouraging. A carbon block filter would be much better than dechlor. Ammonia and nitrate removers chemically bond or mechanically trap these waste products. They can release them too. Short term in a crisis, they might be handy, but down the road, they will bite you back.
A sump, isolation tanks with sponge filters, water movers, a marine lighting system with a moonlight function and timer, and live rock are things to add to your list. The power heads, freshwater aquarium lights, and canister filter should be deleted. The UV is not essential.
Someone suggested a heater. No way. You are trying to export heat from a marine tank. Lights, pumps, and powerheads or water movers are already adding lots of heat. Sometimes you need a chiller, but never a heater. Skipping regular water changes is also bad. Fish develop hole in the head disease when this is neglected.