well I have some things to ask and point out... (to my very limited knowledge but I think I'm right anyway)
first of all, wouldn't the vikings be kind of important in the dark ages? and what do you mean by celts?
second, I think chazars would be khazars. and burgundy in the dark ages? I'm by no means any historian, but the others on my team are into it, so if you need some ideas you could visit my mod (sig)
and most important, will you make like 3-4 games in one? because I believe there are a faction limit of 21, and you have already filled up 16 spots. I think you want to take a look at
http://forums.totalwar.org/vb/showthread.php?t=42905 for things you should know when planning factions, units etc.
you could solve this by programming some copying one sub-mod, for instance dark ages, over a high medieval sub-mod. but making all these mods seems like hell of a lot of work to me :sweatingb
just trying to help you think about how to pull it off