Far as RO
Water, many well established fish stores have told me they dont use RO
Water... it all depends on the water coming out of your tap... Then again if your going to spend 40+ bux on a fish might rule bad water out from the start...Selecting RO
units are a whole nother debat, let me know if your interested i can dig up a few post I had regarding the Ebay 100 units vs nonebay 200+
I am also new to salt water, my 40 gallon tank is about 7 months old now.... Dont rush into buying fish until your tank cycles, throw a raw shrimp in the tank, and keep loggin the levels.
Far as a skimmer, its not required, but it makes things so much easier.. the Empier 400 will work, but over time u'll the filters will get dirty and u'll need to clean them a lot....and eventualy u'll prob want to ditch it.
Other than that, only advice I can buy is take it super slow, my tank took like 6 weeks to cycle... I kept doing water changes, adding rock, you name it..So it delayed everything. Also buy 1 fish at a time, and let your tank adjust to the chang in the bioload... maybe wait 2-3weeks before u buy something else...
A local store had a 30% off sale, so i figured i'd take advantage... well I lost 80bux 6days later when 2 of the 3 were dead.
Far as water movement this I am still strugling with this myself, . but u dont want all your sand blasted all over the place, or the fish being whiped against the glass... if you can find the point just below those two thigns happening you should be okay...
Any other questions just ask