gutters, seamless require that metal extruding machine that only roofers/gutter people have. I have not seen a NON seamless gutter NOT eventually leak at the joints. So, I would definately forgoe a few extra bucks and have the seamless gutter installed.
Now, most facia and soffits fail due to mis mounted gutter systems and ill placed roof edging material. If the gutter is placed right and it catches all the water and water does NOT sneak between the facia and the trough, organic material like wood will work for you. Painted and touched up, you will see years of service.
I am not a believer in synthetic siding, but if I was in todays market and tech, I would definately go the vinyl material. Holds up good to natural occurances and will work nicely with the sun's rays.