I think you have the basis of a really lovely idea, but are being unrealistic in a number of ways.
I think you should look into setting up a free school, and you are going to need to employ qualified staff.
Also, you should look into teacher training yourselves, then you could be qualified staff.
Also, opting out of modern education because you dont like it is not necessarily in the interests of the child, because the qualifications needed to have choice in your life are those acquired through mainstream education. Archeology and astronomy sound like lovey GCSEs, but in reality they are hard academic work, and I am not sure this is what you are looking for
I think you need to commit to a certain number of specific GCSEs, say, 6 maybe, maths, English, 2x science, and two more
There are theatre schools that dived the week up, 3 days academic learning, 2 days theatre, or there are dance and music schools that divide the timetable up, mornings are normal academics and afternoons are something else.
You could maybe do that? Have part of the school timetable for academics and the rest for your pagan, outdoor, forest school type things?
Do any of your community speak a modern european language? It could maybe be a bilingual school? French/ English for example,
I think you are trying to set up a lovely school where children will be happy and fulfilled, and I am sorry, but in reality, children dont like learning much, a lot of the time! and they still have to do it.
I hope it works