Bottom boards are personal preference really, some use them, others do not.
Bees are pretty resilient and the British winters hardly exist nowerdays so you might opt for only using it when really bad weather as the heat will remain trapped in the hive anyway. Probably windy days (especially with my coastal location) are the time I would use them as eddies under the box might disturb the hive.
Having looked at your photos, your hive looks really good. There are two non essential things you might consider, 1) a little landing board underneath each entrance 2) some beginners add a strip of wood down each side of the top of the hive at the level of the ends of the top bars, running from each end board to the other end board. This stops you knocking the top bars when replacing the lid, especially if it is a heavy one. Then then even my fabric covered 4 footer is a pretty bulky thing to move around.