Well, my specific questions regarding the three Electra bikes were answered by e-mailing Electra directly. Their reply:

Thank you for choosing Electra Bicycles, I hope all is well. I copied the axles specs below. I hope this helps, ride safe!

Townie 1 Front: M9 Rear: 9.5mm (3/8”) x 24 Tpi
Townie 3i Front M9 Rear: 9.5mm (3/8”) x 26 Tpi
Cruiser 7D Lux Front: 9.5mm (3/8”) x 26 Tpi Rear: 9.5mm (3/8”) x 26 Tpi

So, for threaded axles, everything BUT the coaster brake is ⅜ x 26 and the coaster itself is ⅜ x 24. I don't care about the M9s because they're already quick-release.

FH