1) See Bike Friday
I commute 26miles daily on a Stromer (coming up on 15K miles); rain, snow ... so I've got some ideas about what works for me ;> A couple of days ago, we scored a pretty new Tern Vektron D8 for my son (it's a folder with the Bafang M400 .. pretty similar to the Bosch mid-drive). The battery isn't integrated into the frame; but like many Bosch powerpacks is somewhat integrated (as opposed to my Stromer, which is completely encased by the frame.
I don't particularly care that the battery is or isn't visible. Time will tell if being external is problematic in rain, but based on the tightness of it, and connections being well protected I'm cautiously optimistic that will not be a problem.
The Bafang battery is a bit harder to remove than the Stromer (although that could be a lack of attention by the previous owner); normally I remove batteries when transporting a bike by car; I had no trouble lifting the Vektron into my wife's car without removing the battery (it is heavy for a folder, but a lot less heavy than my Stromer).
Hard to judge based on my first 10mile ride; but I fear the original owner may have damaged the battery. We will have to see. My wife's Haibike has a similar Bosch system, and that comfortably does more than 30miles with assist at reasonable levels.
The Bafang is rated at 80nm of max assist.
The Tern rides nicely without assist; it's a bit more stable/easier to mount panniers to than my aged Dahon Speed P8. The headset is a bit more adjustable which is a nice touch. Unrelated to design issues, the factory warranty for frame and such is only good for the first purchaser which doesn't suggest a large amount of confidence from the factory ... but I can imagine that protects them from user abuse (previous owner(s) ;>).
If you want to PM me the link to your questionaire, I can provide my perspectives for your project Requirements.