The whole fixie thing is a bit of a fashion statement. If you are an experienced, hardcore messanger or a racer wanting a winter training bike, then go ahead, but as a newbie who wants transportation and a bit of off-road playtime, it is just the wrong bike.
Do you need to carry any luggage or shopping around town on a rear rack?
Do you want to protect work clothes from dirty splashes with fenders?
I would suggest you look for a bike with no suspension, clearance for fat tyres and studded winter tyres, threaded eyelets for luggage rack and fenders.
If you want to convert to singlespeed or fixed or hub gears at a later date, look for a frame with a suitable chain-tensioning arrangement rather than the std Vertical Dropouts (ie, horizontal dropouts, track ends, eccentic bottom bracket or sliding vertical dropouts). I would also suggest using disc brakes for a grimy New York winter.
My Dahon Cadenza does most of that (and folds).
I am agnostic on the 700c vs 26" wheel argument and on steel vs aluminium. I use and like both and really dont care which I ride. I have left steel bikes outside 24/7 in salty environments with no corrossion issues.
A std hybrid style bike will solve most of your problems within budget and is the easiest to buy. Sportier cyclo-cross style models are really a hike in price.
Budget for accessories (lock, lights, luggage, repair kit, helmet)
Do you have any storage issues?

Do make sure you get the correct size.