I wish I could tell you the brain pain will end shortly but mine hasn't since I began reefing 5mos ago
Saltwater Tanks for dummies was a good resource I used to get started.
I use instant ocean though most mixes are fine.
You will find that the more you research the more you will realize that NO-ONE has direct conclusive information beyong the basics. Filteration, and lighting can be performed sooo many different ways!
I can tell you my experience, which isn't too extensive so slap the two cent value on it and read way
Live Rock is the best natural filter a reef tank can have. I have 65lbs of Live Rock in my 46Gal bwfnt. Since I do not have a sump/refugium providing additional water volume (good for stability) water flow, and biological filteration I use a mechanical filter as well (Magnum 350 with carbon). This keeps my water clear. The organisms and Good Algae within the live rock perform biological filteration. A wet dry filter performs both types of filteration (biological&mechanical) though I have read that the bioballs can become nitrate factories over time (Nitrates not good). In a nut shell Mechanical filters physically remove waste/debris in the water whereas biological filteration are organisms that feed on the debris/wastes. Live Rock is my favorite aspect of my tank at this point because of the bio diversity. It is also a must for housing a plethera of saltwater inhabitants.
Adding critters to your tank should ocurr after you tank has gone through the Nitrogen cycle. Read the online or printed literature on cycling a tank. Adding live rock in the beginning will help along the cycle and allow you to cure the rock without harming any critters should you wait to add it later. As far as inhabitant goes they will come after the cycle, usually starting with a cleanup crew that will eat bad algae and detritus (wastes) they usually include snails, hermit crabs, starfish..
As far as grouping corals, inverts ect.. each critter has different attributes. Some require more space while others are not territorial. Some are toxic to others while some may be a natural food source for another.. Point being you will want to learn about each critter before adding it to your tank.
Well that covers about .02% of the info on this hobby but don't get too overwhlemed. The stuff you learn about ecosystems, reefs, critters etc is very rewarding and interesting! You will find reefers with more algae than water loving it as well as guys like mojo reef who construct masterpieces the truly replicate reef life!
Hang in there!