Single-speed or Internal Gear
John,
You ask some good questions. Regarding the single-gear or internal-gear hub, I have both but use them differently. I've got a Marin San Anselmo (only made for 2 years) with a Shimano 7-speed Nexus hub and 700c wheels This is my main ride for all local errands and it has a rack and pannier. The gears do help when loaded up but I wouldn't worry about using a fixed gear to replace it unless I regularly had to climb steep hills. A downside of the Nexus is that it's even worse than a fixed gear if you get a flat rear tire. Both the shift and brake cables need to be removed and not one bike shop, including the place I bought it, has gotten things right the first time after a repair. That said, I noticed that Harris Cyclery is offering a specially modified Bianchi San Jose with the latest Nexus-8 speed hub, making it a quite unusual touring-type bike.
No matter what you buy, I'd put really tough tires on it before it ever leaves the shop, and I'd opt for a steel frame ride every time.