120g to start, thats great. here are some other things to consider/ suggestions to start.
VHO lighting on electronic ballast, 1.5"-3" max of substrate, use "oolithic aragonite", 1.5lbs per gallon of liverock, use "dead rock" or base rock for anything under the sand, setup a refugium, use a skimmer that is rated close to twice your water volume, use a quality needle wheel type skimmer, parabolic type reflector for lighting, rodi unit, turnover rate of 10-15,
vho lighting because it's not as hot, extended bulb replacement, can keep corals, less electricity. less substrate because it may go stale when going too deep and besides it's easier to add then to remove. use base rock where you can because it will be covered by sand etc. and it's cheaper. love a refugium for nutrient export and biodiversity and natural food source. needle wheel type of skimmer because it usually uses less electricity than a beckett that needs a pressure pump. a good reflector to make use of all the light output. rodi a must. water flow is good but random/variable is better. try to keep your pumps external, very efficient powerheads or closeloop system and add fans where needed like lighting and indoor temperature reasonable should prevent you from purchasing a chiller.
you should be able to keep a diverse of low to medium light corals like mushrooms, tongue/plate corals, brain, toadstool/leather/colt corals etc. and your typical reef friendly fish like tangs, clowns, basslet, etc.
always include your typical snails, starfish, hermits etc. to cleanup the tank.
testing water and stock knowledge and stocking order is also a good idea. I am sure I missed some stuff so
