Since each pair of rafter creates there own void or individual air space can you vent sideways through the rafters into the sofit area. I don't want to drill upwards through the metal roof for each void. if you can vent sideways what size hole would be required for a 16 ft long 8.5 inches deep 14.5 inches wide area
This is tough to answer - I face almost the same dilemna as you.
Yes you can drill holes in your rafters - but only a little and within careful guidelines.
These guidelines are meant more for drilling holes for electric wires etc. and may not be applicable to the more numerous holes needed to enable cross venting.
You at least have a pitched roof which would allow for a ridge vent - why not that?
Another way that I'm considering is make a 3/4 inch gap below the rafters with cross strapped furr strips and placing the insulation layer/ceiling below that.. The downside is that insulation has to be removed from the rafter bays. The new location of the insulation/ceiling below the furring drops the ceiling down.