Dual drive uses 135mm dropout. I don't think it's possible to reduce the width. I think I read somewhere that the axle threads are 10.5mm diameter, so you probably won't be able to find thinner nuts or cones.
Doesn't look like Tern uses normal hangers?
https://www.ternbicycles.com/us/gear...illeur-adapter
Dahon uses somewhat 'standard' hangers that can be bought cheaply with the Marwi Union brand for $3-5.
MARWI | Gear hangers - Dahon
Some people on the forum use 11-36T 10 speed cassette with the Shimano Zee RD and a single chainring. That would give you 327% range.
On my Dahon Vigor, I use 12-34T 10 speed cassette (custom mixed cogs myself) with 24/44T double chainring for 519% range. The RD is Shimano 4700 GS which has the widest chain wrap capacity of all the Shimano GS road RDs.
Front derailleur used to be the 4700 FD, but it broke down and I recently replaced with with a SRAM Rival YAW FD, which works much better, but still needs some bending of the outer cage to get it a little bit wider, depending on how you're setting this all up. I simply used my old Shimano FD shifter, because the way I set it up, I didn't need trim position, so I simply needed a trigger with 2 positions. The 4700 trigger uses a long pull, so I had a lot of cable slack to work with. There was another thread somewhere discussing this.
https://www.bikeforums.net/folding-b...eat-tubes.html
You'll find photos in the thread above of how I setup my FD adapter. I used the LitePro P clamp (41mm diameter) but attached my own 3D printed steel adapter because the adapter that came with the LitePro P was too far rearward and angled a bit too far backward for me.