Thank you everyone for their input on wheel size, I'm sticking with the real 16" (349) in the shape of 28 hole Velocity Aerohead rims. Seems to be more sensible as I at least know the tyre choices from almost 7 years of owning a Brompton.
Pixel/Huw - one more question, do you happen to have the official wheel building dimensions for the 74mm Pantour Delite Suspension Hub? It looks to be symmetrical and I've measured the width from center to flange to be 23.5mm & the diameter of the flange to be 52.2mm, spoke holes seem to be 2.8mm. Just want to know I'm on the right track with those measurements before calculating spoke length.