Bill Tindall, E.Tn.
What is the objective of turning the trees into floor? The trees were there before they were blown down and maybe lots of others. Why now for these trees for this use? Not a "dumb" question because the answer determines the advice.

Beech is a common tree in many woodland locations. Yet, beech is a worthless timber species except occasionally it is sold for RR ties and pulp wood. It has been used for industrial flooring in the past, but I have not see beech flooring for sale in my lifetime. What ever the motivation to use these trees for a floor needs to overcome the reason(s) nobody else uses beech for this application.

To specifically answer your question, the size of the room is irrelevant. Cracks will open and close to accommodate seasonal changes, if it is installed correctly.

Any experience with European beech is largely irrelevant to this application.