Well...you'll need an overflow, you can buy one on-line (stay away from CPR), some drain line a pump and some return line. Depending on how fast a flow rate you have, you may want to glue in some baffles and or make a dam and weir, to prevent micro bubbles from returning to the tank. It is fairly straight forward. If you have enough LR
in the tank, there is no need for any additional biological filtration, so the bio chamber would be unnescessary. If it was me, I'd use the 20, you'll be able to keep it more full than the 10 giving you more water volume and if you feel like it, you can turn the 10 into a refugium, adding to the nitrification and denitrification capacity of the tank, as well as provide free food for the fish.