You would be over stalking a little bit and sometimes that works me personally I would try 10 - 12 or 12 - 14 slightly over stocked reduces aggression plus more fish just make sure you get him around the same size as the others or they will kill him and of course rearrange the aqua scape give him a chance
I'd say no. The fish u have in the column tank will already harass each other badly eventually. With cichlids it's not so much the gallon amount as the length/footprint. A standard 55 gallon with the bigger footprint is better than a56 column with small footprint and height. Kenyi and auratus are super hyper aggressive too.