I've been out of the bike commuting game for 3 years now and I'm not happy about it. For two years I did a 11mi round trip year-round in Boston, and slowly acquired the clothing and traffic skills to make that manageable. Three years ago I moved to Philadelphia and am fortunate to live in walking distance of work (1.0-1.5 miles depending on the day). So my two commuter bikes (a road and an MTB, neither very commuter-friendly...no fenders, no chain guard, etc.) in Boston have slowly degraded from sitting outside without much TLC and I've sold them off on Craigslist to start afresh.

I'd like to have a single bike that makes it as effortless as possible to hop on, bike a mile, and hop off. I won't ride it in anything too icy (probably going to list my studded MTB tires soon if anyone's looking :-) ).

From past experience I know I want:
- Fenders
- Rear rack
- Chain guard, completely enclosed if possible
- Fairly inexpensive so I don't have to worry
- Non-QR skewers
- Road tires

And I know I don't want/need:
- Folder
- Lots of gears (6-7 would be fine, with 3 ok if it's the sweet spot and 1 ok if I have to). I have a bit of an irrational desire for internal hubs at the moment....
- Fixed gear (single speed would be ok)

So I guess my question is about strategy. Budget is something like $400. Should I aim to buy a Craigslist fixie/SS with braze-ons for the rack/fenders and then upgrade the drivechain later? How do I even tell if it's fender-compatible (I know my way around a bike toolbox, but I've never installed fenders)? Should I go instead for an old 3-speed and upgrade components as there's time (downside: my comfort zone is entirely around stuff built after 95 or so...I like allen wrenches!)? Or something new designed for commuters (most of which seem to have mediocre 24-speed drivetrains rather than nice 3-speed enclosed trains)?

Oh, the angst.

Thanks guys.