I am wanting to add Mikrotik 2.4 with a 15db omni to my already existing towers that have a 2.4 AP with a amp and 12db omni. What type of spacing (physical and channel) should I use to get this to work good. Also, The reason I am adding this mikrotik is because I have overloaded my other AP with 40+ people. How many can the mikrotik handle with a decent radio card?

hi, switch from omni to sectors, in this way you have your amplified radio on 120 degrees sector, and the new AP on another 120 degrees sector (you may possibly add a third AP with another 120 degree sector antenna) allowing you to have 120 to 180 concurrently connections).

If you must use omnis use one on channel one and the other on channel 6 but since its just two omnis then use channel 11. I have not had problems with spacing as long as its about 2ft apart on the mast/tower.