IMO the order of back story and theme should be:
1, Pick a nation - Kind of self Explanatory.
2, Pick a Territory (optional) - Different Territorys have different things about them. Different outlooks, climates, ect. Also the history of that territory will have a big influence on the group.
3, Do you have a focus in a certain field? Are you all mages, fighters, scholars, wandering priests, mercenary’s, family, refugees, ect.
4, Each founder should now work on their own backstory. Something simple. Start with:
Where your born and grew up (not the same place possibly?)
Where you are now.
What’s your profession (Skills don’t have to come into to this)
Are you tied to any recent history in the area?
How do you know the other founders/other significant people (You may only be representatives of a much bigger group? Does the head of your steading not come to anvil to better look after it and instead a proxy?)
5, Carrying on from the last point, why did you decided to stay with the other founders/group and how did it grow. Is it old, new, temporary. Does it have a specific aim? (Recover valorn territory ect)
6.Fill out the bits. Remember that empire only happens for 4 weekends, where as the group will exist between them. What do they do between?