Honestly, no one can fully walk you through it her. People write whole books on doing what you are doing.
There is a plethora of needed and optional equipment. Everything from filters to lights to the fish themselves! You are best off going to the local pet store like a Petco.
When it comes to brackish aquariums, realize you will be spending a lot of money. They need constant attention and surveillance. They are not like they appear. There is a lot to consider. If you thought a marine tank would be like fresh, you are off.
Your fish will need filters, temp monitors, heaters (because tropical fish are popular,) lights, and possibly feeders. That is just among things like gravel, sand, coral, plastic ornaments (optional) and plants.
I suggest marine aquariums for dummies. It is an in-depth book, and good for beginners. It has a lot of information. Still keep in mind, it can be more clear to go to a pet store, and speak face to face to have all questions answered. This way, you can get good deals and try to go into it prepared.
Good luck.
