These are my hives. Its all I can realistically keep in my suburban bubble neighborhood.
I have read many places that keeping entrances in the center on the long side, splits the box. The problem (as I understand it) is that the queen keeps the brood nest in the middle near the entrance, and that it splits the nectar and honey, so that in winter the bees starve on one side or the other, seeing they can't/won't get to the opposite side.
Of course, I don't know this to be true from experience. It will interesting for you to tell me what happens as you go through the seasons.
When I did use follow boards (and I might next winter) I kept just one.
As far as keeping a divider board in the middle and housing two colonies in the box, (one on each end with their own entrances), I think that is a great way to use a box. for me, after the first year each colony filled up one whole box itself.