This challenge has a lot of information to it but otherwise it plays like a normal game.  With a few exceptions,  For one I like to have a mortality rate.  This is totally optional to you as the simmer. but I like realism and Medieval life was difficult and often short.  In my game Death can occur from exhaustion(5% chance when they pass out), Illness(thanks to NRAAS Vectors), or Childhood Accidents/illnesses(check mortality section below)  I also like to use Woohooer to determine my sim's fertility rate.  You can set this per sim or just for your matriarch(mother)

When you start this challenge I like to start with a founding family.  They can be human, fairy, werewolf, vampire, whatever you would like and their aging system can be as short or as long as you like.  I recommend Normal or Epic especially if you use a pregnancy mod that extends the length of the pregnancy beyond 3 days.(like me).  At the beginning you start in the peasont class...the lowest class in the whole system.  You will gain rank the longer you play(several generations) and by reaching the prerequisite's for that rank listed below.  

You may start in a pre-made TS3 home or make your own(highly recommended)  If you start on a pre-made home remember to remove all electronics like radios and TV's.  And I'd suggest redesigning your walls and flooring to be period specific.  I also recommend removing books as peasants rarely could read.  This will change as you progress through the ranks.