lol didnt see the posts on the 2nd page sorry.
If you are a bit low on money then take Tre's advice.
the main point is flow. the rock is the main filtration.
Chemical media are the pouches with stuff such as active carbon in them. I use chemi pure cuz it can keep the water free of nitrates in a small tank. I endorse no addtion of CHEMICALS into your water lol!. I simply mean the media that acts chemically on your water to adsorb bad stuff like nitrates, phosphates and stuff from livestock.
Your main concern while starting is the live rock and flow of the powerheads. This is why I said to worry about the chemical media stuff only after youre done cycling the tank, and youve stocked it with some livestock.
the chemical media gets put into the HOB filter because thanks to the filter, the tank's water is able to flow over the media and the media can take out impurities. idk why I'm explaining this in such detail cuz its the same exact concept for FW tanks, which you should be more than familiar with thanks to the 70 gal
To start here are the necessary things:
A tank (lol)
Premixed water (by you so you know exactly what you want)
Refractometer (so you can measure exact salinity/Specific Gravity of the water)
Heater(s)
2 Powerheads (for water movement)
Base rock (to provide living places for the bacteria that you will be culturing in the cycle)
Live rock (to provide your initial bateria and sometimes die-off to start your cycle)
Sand (not really necessary to cycle, but since you got it already you may as well get that out of the way and add it to the tank when you begin)
Market Prawn in container with holes in the lid (provides ammonia for bacteria to grow)
SW test kit
Thermometer
Top Off System - you should be thinking of this one, unless your tank is very well covered and isnt open-top. evaporation will change salinity rapidly if you do not top off and will kill livestock and bacteria thus crashing your tank.