If they are all going to be new to the coop, then the only issue you have with putting them all in at once, is the possibility of cross infection if either group have any diseases/parasites etc. If they are coming from the same source, that is less likely but still possible. If I were in your situation, I, personally, would put them all in at once but I am sure you will get differing opinions....it's personal choice really.
Most integration problems are as a result of a new group joining the established territory of an existing group which is not the case here. When I got my six girls, I got them all from the same breeder but she had separate breeding pens and I have three different breeds so they had never met each other or even seen each other through a fence.
When I got them home, I put them all in together and they immediately behaved like an established group does when in a new coop....they huddled closely together in a corner for a while and then gradually began to explore as a group, with a 'lead' bird showing the initiative and the rest following suit. This 'lead bird' was one of the cochins who, for the first two or three days, was first to go anywhere or try anything new and the rest followed, but within a week, a different girl, a brahma, had taken the lead and is now the dominant hen but the whole process was remarkably easy because there was no pecking order to begin with so everyone just kind of slotted into place.
