>When you use a follower board, does it just take up the top space that would be occupied by a frame?
No. It depends on how thick you make it, but if you make it thin, it takes up the space of about a half of a frame.
>When I bought nucs this year, they came with what the supplier called follower boards which sat on the rim where the frame sits and occupied that frame width - there was nothing below the top "follower board" and the bees in the nuc had built hanging comb from the follower board -
A follower should be the size and shape of a frame only it's only 1/4" thick or so. When you leave a 3/8" space on each side it takes up about an inch.
>The point being - if I used what I was told were follower boards, wouldn't the bees fill the space below with comb?
If it's just a top bar and not a sheet that fits in like a frame, yes, they will just fill the space with comb.
>Also if you are putting 9 frames in isn't that challenging the advantage of the lighter weight of the 8 frame equipment?
No. Bees fill the space with the same weight of honey whether you put 9 frames, 8 frames, 7 frames or six frames in an eight frame box. the box will weigh the same as the bees will still fill it with honey. Less frames makes thicker combs. Actually the six frames will be slightly heavier than the nine frames because there will be only seven 3/8" beespaces between otherwise solid honey instead of ten 3/8" beespaces between otherwise solid honey..