Well i have a 20 gal fw
hex and a 60 gal fowlr
hex. We just like the way those tanks look. Honestly if i had it to do over again i would have went with a rectangle or bow front tank for my saltwater as they prefer to swim long distances laterally as opposed to the verticle nature of this tank. Its an awesome tank for fw
though! The protein skimmer isnt a must but never hurts. I dont run a protein skimmer on my tank. You just need to be more attentive to your water parameters. Get a test kit for ph, ammonia, nitrates, and nitrites. The smaller the tank, the less forgiving it is. The biggest challenge with a hex is hiding all the equipment on the back. You'll need to be creative with your live rock so that you see the aquarium life and not, filters, powerheads, heaters, uv
sterilizers, and cords! My plan for this hex is to convert to a fw
discus tank and upgrade to a min 150 gallon reef tank. Just not happy with the hex for saltwater. Someone else will have to give you advice on stocking. Im not sure whats compatable with corals. Ive stayed away from corals because they sound like alot of work and need special, very expensive lighting. Good luck!