If your facing the tank the rear chamber to the right is chamber 1. There should be a tab on the dividing wall between chamber 1 and 2. You can cut that tab for added flow. Go to Intank.com for chamber fuge and media baskets. Youtube has tons of videos on how to mod the BC. Good luck!
PS If you have the $ and want to do this right you'll find these tanks are far from all-in-one. I have an Aquaticlife 115 skimmer in chamber 1, Intank media and fuge baskets in chamber 2, JBJ nano led on the back for the chaeto (had to scrape some of the paint off the back of the tank so more light could get in), a heater and Tunze 3155 ATO in chamber 3 (ato essential for a nano tank to maintain salinity as well as water level for the skimmer), an MP10 for flow and a Tru-Lumen 3 LED blue moonlight attached to the bottom of a DIY mesh screen top. Love the tank but definitely not all in one.