The only requirement is that it has to be an all-weather bike.

Frame type. Road? Hybrid? Specific model? New? Used? (you
pick but I prefer used)

Wheel size. 700C? (Yes, this is my choice)

Drivetrain. Derailer? Geared hub? (either one will do)

Brakes. Standard caliper or V? (yes, easy to maintain)

Storage: Rack+Panniers? Baskets? Trailer? Xtracycle? (all as
needed)
Fenders & rack? (YES! A must have.)

I'm also VERY interested in this type of bike altho I don't
think a bike like this is new by any means. Most folks'will
"run what ya brung" as a utility bike.