what part of the interior layout on the universal cottage cannot be changed? we know the stairs, but is there anything else?
If you use the I-joists for the floor system the walls are all non-load bearing and can be moved or eliminated.
If you use the beam and standard joist floor then you need a beam line at the inside of the stair but these can span between posts and need not be under walls.
Thus both floors can be open without interior walls if needed. Just the stair.