I'm not sure if Rolf makes 20" rims? (Anyone know?) I do know that Velocity makes 20" V rims and Aerospoke also makes streamlined (although heavy) 20" wheels.

In my humble opinion, the occasional bunny-hop on folding / separable bikes is fine, as long as the bike in question has suspension (like most you are considering). However, many Terns and Dahons do not have suspension, therefore I believe a bunny hop would apply considerable stress to the folding hinge mechanism. (Again, just my opinion... not meant to be a slam on Dahon or Tern by any means.)