A 6 ft tank is a good size to start breeding especially with the species you have listed. From the list if you are new to spawning cichlids I would pick either the Parachromis Multifasciatus or P. Friedrichsthalii (Loiselli) as generally these are more tame and mild mannered compared to the Amphilophus Saggitae or the Herichthys Carpintis.
It is going to be harder for you to spawn these if you have already grown out and have larger males. Adding a female to a tank with an established male can be dangerous for the female. I’d recommended using a divider. I personally prefer to purchase 10 juveniles and grow them out together and allow them to pair off naturally then remove the extras.
At the end of the day though you should choose what species you enjoy / like the most and start with that.