Just thinking about this thread overnight.I would probably book 7A for now rather than 5F. There will always be a middle seat available somewhere, whereas the windows are the prime pick.
You may change you mind about the mini cabin and window seat later… in which case if you reserve your seat there now you’ll have it, and if you really want a middle seat in the main cabin later you should not have any problems. The other way around (5F Now trying to get a window later) could be difficult.
The middle seats really have no advantage… window seats have more sense of space and privacy, and you get to control the shades (handy for watching IFE or if you want to snooze).