OK, as I have stated before I am going with all mediums for my hives. Should I use the 4.9 foundation in all of these, brood and surplus honey? Can you extract honey from these small cells? Should I stay with 10 frames instead of using 9 for the honey supers?My opinion
All mediums is good. 8-frame mediums is better.
You can use small cell beeswax foundation wherever you would ordinarily use beeswax foundation, for brood or honey. You can extract honey from small cell comb. If you stay with the 10-frame width, instead of going down to 8-frame you can trim the end bars on your frames to 1-1/4 inches, then you can fit 9 frames into 8-frame equipment.
If you stay with 10-frame wide supers, you should keep a full set of frames 10 or 11 per super, if they are mostly just foundation. Once the foundation is drawn you can remove one or two per honey super and the bees will expand the cell depth to hold more honey.