SunTuf panels (which sound pretty much exactly like what you've got, just a different name) come with plastic (not foam!) spacers, and without them our roof panels would NOT have worked at all. Those spacers took up a lot of the load.
Our directions said to attach the foam/plastic things to the purlins with nails (we used #10 screws), using every other 'valley'. Then you go and attach the roof panels themselves to the spacers with hex screws or similar -- on the peaks. Though there was at least one corner where we had to attach the roof panels directly to the valley as well, for extra strength.
Our entire structure is 7' long and we used 4 2x8 8' rafters, cut on the diagonal. For 9', depending on whether you have to plan for wind and/or snow and so on (we did), you may want to use as many as 6-7 rafters, I give you that # based on how well our roof turned out.
HTH,
Whitewater