Must-haves:
Fenders, chainguard, internal gears, disk or drum brakes, hub generator, rack.
Schwalbe Marathon Plus tires in the summer; Nokian 106 Haks in the winter.

A trailer is good for dropping off kids on the way to work, snagging groceries. When I don't need to do this, I leave the trailer at home and carry only a U-lock and rain gear.

Probably cheaper to start with something like a Utopia, Kettler, a Breezer than with a recreational bike. In particular, chainguards are hard to find.

Paul