Will do regarding the mini-velo. This is my first complete build from the ground up (even the paint) and it's being spread out. Some of it is quite frustrating, such as needing an extra-long chain because of the 18.5" chainstays.
As for your folding bicycle, the biggest improvement you could make would be switching out the telescoping/QR handlepost to one that is a single piece with integrated, non-QR clamp. Finding one of these that's the correct height for you might take some time. An advantage of the Dahon is that aftermarket parts are quite available, even on Ebay. That's where I found the new handlepost for my Dahon.