I find internet better than most books. What you need will depend on the type of tank you want, remember buying something of a better quality is better than buying one and needing to upgrade later.
You will need a refractometer since most hydrometers aren't very accurate and a good test kit get your own liquid test kit don't depend on the lfs
for test results.
unit I consider important because it saves me hours of running around getting water for my tank. Always start your tank right with RO
water so you hopefully won't have the horrible algae outbreaks others have had.
The rest of the equipment will depend on what you are wanting in your tank. Any light will work for a fish only tank if you are going to do things like coral, anemone, or clams you will need a good quality of light.
Part of the filtration of saltwater tanks is live rock and sand. Figure between one and two pounds per gallon. Research and figure out what kind of fish you are wanting some fish need deep sand beds to sleep or even live.
Skimmer would be nice finding a decent hob
skimmer is nearly impossible for me.
ATO is nice to have but you can always top off once or twice a day.
Setting up the tank properly will make a big difference in the years to come. Take your time because only bad things seem to happen fast in saltwater tanks.