Hi Wayne
No expert on this as I’ve always been latex printing but since you’ve not had any other replies I thought i would have a stab, might generate some response if only to correct me LOL
1/ I think all colours fade at the same rate its just the lighter colours will look like they fade quicker because they don’t have the colour depth the darker ones have.
2/ Polymeric in my opinion is more about the quality of the vinyl, less shrinkage and longer period of material breakdown compared to monomeric. The laminate might protect the fade better due to being higher quality and also more lightly it has uv protection built in than a cheaper monomeric product.
3/ So long as its a reasonable quality monomeric and by this I mean 3-5 year product like LG / MD3 I would think 2years before fade starts and shrinkage becomes apparent an 3-4 years before fade is very noticeable and materials starts to break down. This could be very variable though depending if its in direct sunlight or away from the sun.
As stated above this is just my opinion based on what I’ve seen I would not recommend you use my thoughts as set in stone when making a business decision on what product to use.