Control 16 outlet plugs and RGB led lights

I have a Mega2560 that is programmed to control two 8 channel solid state relays that controls 16 outlet plugs for standard Christmas lights. I want to add the RGB pixel lighting to my program. I am very new to this. Is it easier to get more Arduino boards and program them to control the pixel lights or can I add programming to existing program to run the pixels along with my outlets? I am using 16 channels of 48, would like to use this board if possible.