I'm jealous and i've only just got back from a holiday!!
I've been to New York but not while preggers and you probably will walk around alot but i seem to remember cabs weren't too pricey (but then i did go a few years ago now) and they have a metro too. At 22 weeks you should be ok, not too big, are you feeling ok at the moment energy wise? Hopefully you'll have lots for shopping LOADS as there are soooo many shops and good sightseeing to do! You'll have so much fun!
Just take regular rests and stop at the many coffee shops for a break when you need and get someone to carry all your shopping (even if you are ok, blame it on the pregnancy he he he)!
Weather should be similar to here so take some warm clothes. For the flight if you have space in hand luggage i'd recomend an extra pillow or something to support your bump if you try to get some sleep on the plane for your side as i was a little uncomfy after 7 hours in various different positions, but not too bad at all really!
Have fun!!!