To answer your question about Brooklyn; No. Brooklyn Nets won't have a strong fan base IMO for another decade or so. I believe team affiliations are usually formed at a young age and based on what you can watch on tv. If you live in Brooklyn now you probably grew up a Knicks fan. Allegiances don't necessarily change because a former rival has jumped to your city. The Nets are growing their fan base now, as the kids in Brooklyn are growing up into a group with spending power. It will still take years for that to happen.
I grew up in Manhattan in the early 80s, the Knicks were on Cable TV, my dad could take me to MSG on the subway etc so i became a Knicks fan. As i got older some of my younger friends however became Bulls fans due to the power and popularity of Michael Jordan. In my early teens when my family moved from Manhattan to northern New Jersey I kept my Knicks fan affiliation (even though the NETS eventually became an Eastern Power and consistently clowning the Knicks) since I was old enough to know what a front-runner (my Bulls fan friend) or fair-weather fan was and I wanted no part of that.
A few years ago I moved to Brooklyn just about the time the NETS made their move to Brooklyn. I expected there to be a strong contingent of Brooklyn Nets fans in Brooklyn but that isn't what I experienced. I see many more people wearing Knicks hats and other gear than Nets gear. In fact only recently have i seen folks wearing NETS jerseys and that is primary due to the fact that the NETS decided to create jerseys that said Bed-Stuy (where i live) and i've seen a couple folks wearing those i suspect out of pride for their neighborhood mostly.
Lots of Knicks fans are Giants fans and Rangers fans. These teams have a long history in New York. Share the same broadcast partners (MSG Network owns the rights to Knicks and Rangers and they run a fair bit of Giants programming too) and even some of the same primary colors. The Islanders are a Long Island franchise, who for similar reasons to the New Jersey Nets moved to Brooklyn to capitalize on a potentially larger following. They have no historical relationship but are mutual occupants of Barclays now. Brooklyn isn't really a hockey town except for then the LIRR brings its fans to Fort Greene and the surrounding environs on game days. There's no reason other than random chance for an Islander fan to also be a Jets fan. I'm sure there are some but again it's a Long Island thing and that's not really the germane to the Jets. I think there is more correlation of JETS and METS fans since they are both franchises that came to their own in the 1960s.
There are those corners of Knicks/Jets/Mets fandom <--- These are the folks to feel most sorry for.
Everything in moderation. Even moderation.
