The only things that were added so far are the new civs. And some stuff from RFCE: Units (+promotions), buildings (+wonders), resources, improvements. (But the resources and improvements were only added to fix the error when you load the mod. They can be left out if neccessary.)
I think that the civs aren't in chronological order because we wanted them in so they can be tested anyway. And move them later. But it's probably better if we order them right away.
I also took the Units and Other paks from RFCE. But I didn't upload them because they were too big etc. But they are indeed needed for now. But to answer your question, no. The leaderheads pak isn't required. (I gave all civs the barbarian LH for now, which has vanilla art)