I am at 9 inches outside width for a 5 frame nuc. I started this way after making 3 one piece 5 frame nucs from a plan on a website - Honey Run Apiaries if I remember right. They have a built in wire mesh at the bottom for ventilation (which can be closed off) and one auger hole at the end. My experience has been that they do not meet all my requirements, as they can only be a bottom when you expand to two storeys. If they get congested there is no bottom entrance to allow more traffic. They were also a little fussy to make - at least with my woodworking abilities. If I sell 5 frame nucs next year I may sell them off to customers.
However, they did influence the rest of my nucs as I stayed with 9 inches as the outside width dimension. I have a 3/4 hole three inches from the center of the top and this winter the biggest improvement has been "OD Frank" handles - a cleat on the end of the new boxes I made with a 15 degree slope that really tucks itself into your finger tips.
I am moving to solid bottom boards as they are easier to make and other successful nuc practitioners don't seem to be using SBB's.
For tops I use FBIC's (feed bag inner covers), some solid migratory style covers or 2 inch insulation.
If I were starting over I may have gone to 8 1/8 width 4 frame nuc boxes (Michael Palmer style) as a single standard telescopic cover will cover a pair of them.