Alright, first thing first welcome to the salty side!
All right now it's time to decide what type of salty tank do you want. Fish only, FOWLR (fish only with live rock) or a reef.
Now if your just starting out then I recommend the fowlr, as live rock is your major source of filtration. With bigger tanks (20g an up) imho a sump is a way to go as it gives you more water volume, a place to put all your a major equipment, an it more customizable to fit your tank. You can always go with hob filter if you rinse your media out regularly also, but this also cuts down options an doesn't control algae as much as it has no place to grow at besides your display tank.
Okay after deciding your filtration, it's time to decide what kind of bottom you want, a shallow sand bed, a deep one, or a bare bottom. These also their own cons an pros also your own personal taste. I usally go with a shallow sand bed as it has less of chance to trap pockets of gasses an other things. Also some animals need a deeper sand bed in order to be kept so your stocking list is also a factor
Now if you go with a reef, then lighting is the upmost importance besides water quality. This is not needed right off the bat as your tank needs to mature to have a reef tank.
Now equipment wise, powerheads,
A quality heater, lights, salt, skimmer, sump or a filter, assorted media like carbon, purgen, gfo, reactors, ri\di unit
Now if you go with a sump
.filter socks
In sump skimmer
Stuff to build a alage scrubber if you want
Then you have misc. items
Like airline tubing
Throw away cups to thaw out frozen food
Various scrubbers
A paint scraper
Extra buckets
Spare parts for your ro unit
*edit
A rodi unit is the upmost importance in the salty side as it can stop major issues in te tank
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