I tangle with a cop every few months over my tripod but the reality is that they can't do a thing in public spaces (and I gently remind them of the laws, an absurdity in itself). The only limiting factor is your common sense and how much you are willing to be inconvenienced. That said, I live here so I sort of avoid Times Square like the plague. If you must have the shot, you are still allowed to take it but it may not be without its annoyances. The only no-no with tripods is in the subway and in private spaces (which may not appear so private upon first glance). My biggest battle has been photographing in the subway. This was a bigger problem five years ago. MANY of the officers patrolling the subway system had not done their homework and believed it to be illegal to photograph anywhere in the system. After repeated interactions, the NYPD seemed to make an effort to educate their members on the actual laws they were enforcing and thankfully this is now a much less common occurrence.
I have been shooting street here with Leica M and Nikon F for quite a few years but lately I have taken to the streets with a recent acquisition, a Bronica SQ-Ai. With a prism and a grip it is just as convenient as 35mm but when shooting people it does tend to get noticed however, not as much as I would have suspected. Now that I'm quite comfortable with it, it seems to put people at ease and I am getting less shots of people staring into the camera.
As to which camera to bring, I think it depends on what you intend to shoot. If you want to capture people and all their little magic moments, that require you to work quickly and decisively (what I consider traditional street photography), I'd certainly prefer the MF rig. If I was more about the surroundings and the architecture the people were in, I would go 4x5. I know some guys shoot street with 4x5 hand-held without flash but I think that's being a bit masochistic! For me anyway, I'm on board with the sentiment that 4x5 is just too darn expensive to shoot without a tripod so I suppose the right answer is that you bring both! Have a good time!