I would suggest you get hold of a copy of Jacqui Wood's Prehistoric cookery and take a look at her websitehttp://www.archaeologyonline.org/.
The book is an excellent resource, giving clear instructions how to make food the prehistoric way including cooking large roasts and making earth ovens outside. She has been providing practical demonstrations of how our ancestors cooked for many years and really knows what she's talking about and what the food tastes like.
I understand she has published a new book recently but I haven't read it yet.
Anthony from Arne Herbs, who posts here regularly, is writing a definitive guide to who introduced which herb when. His view is that many herbs supposedly introduced by the Romans were probably growing here already, otherwise we wouldn't have been able to do much with the few that were indigenous beforehand. (Apologies to Anthony if I haven't given the correct interpretation of previous comments.)
I would suggest you concentrate on using herbs in everyday life - early spring greens, what's edible in the hedgerows and field margins, nettles for food, drink (beers), cheesemaking (substitute rennet when you haven't any calves for slaughter) and fibres (clothes and chordage), cleavers for straining things etc etc. If you want to do some dying demonstrations, contact Kristina May at the Royal Botannic Gardens Kew as she has a lot of practical experience of giving public demonstrations from her visit to the Smithsonian Folklife Festival last year.
There's a really good video on utube which demonstrates making nettle beer in an outdoor trench. I'm sorry I don't have a link, but you should be able to find it by searching.
Let us know how you are getting on with your preparations and the practical delivery.
Very best wishes