Its going to be a reef tank. Probably a reef savvy 65 gallon ghost overflow. All reef sps lps zoas everything to come after. Will have tank stand and sump already. Have an idea of pump and I like CAD skimmers, I have the lighting already. Have rodi unit for other tanks. Should I get ato first, apex ,doser, pumps inside tank,. Heater, chiller,. I am using live rock I have cycling in containers.
Judging by this information, you need testing equipment, a heater, and powerheads next. Then a chiller if needed, depending on your environment. You can dose and top off manually at first and a controller is great, but not needed to start a tank.
As I see it, the order of necessity is:
Tank stocking list (planning ahead helps and will determine what size and shape tank you need)
Tank (stand, sump, plumbing, return pump included)
Source for good quality water
Quality salt mix
Water testing equipment
Rock and substrate (or no substrate...)
Temperature control devices (heaters and chiller if necessary)
Lighting suitable for your livestock list
Power heads suitable for your livestock list
These things are the bare minimums to get an aquarium up and running. All the other additional pieces add convenience. Honestly, you don't even need a skimmer if you do proper water changes frequently enough, but I'd never run a tank without one.
Mac