Wonderful news, glad you are busy.
The first question must be as to what structural load the roof or substrate has been constructed to withstand.
I understand that you want to reduce the amount of pedestals, this sounds sensible, but the issue with only having a few pedestals is that you increase the point load about each pedestal. Yes the pedestal may be able to with stand 850 Kgs but you need to understand if the substrate or roof is also able to withstand this load too.
Longer spans are great and make for a rapid installation, in this case I would advise the use of an (IStructE) Structural Engineer to provide calc’s and sign off the job to cover you for future issues should there be any. This remove the guessing element and you then have something sensible which would then conform with CDM regulations (UK only).
Your second point about whether this may affect the performance of the decking… you may need to discuss this point with the manufacturer of the FRP, they may already may have data to cover your intended use…. if not I would suspect it best not to use this product.
I hope this helps