most clubs and bars nowadays play a mix of all types of music though some are more inclined to a specific genre. understand that in NYC today, hip hop is not as prevelant as it was 10 years ago. back then most of the better known clubs were about hip hop. now you will be hard pressed to find one exclusive for that.
1. without a doubt the best hip-hop spot in nyc for me is bOb bar on the LES. they play a mix of mostly old school hiphop (90s-2ks) be warned this is a very tiny and intimate bar but the music and crowd are excellent. get there before 11 or you will have a hard time getting in. better yet go during a weekday to ensure you can get it. they charge a cover of about 15-20 $ for guys.
there is also wicked willies a little further up north. this is also a great spot to have fun. the music is a mix and its ok but you will find yourself surrounded by NYU students and even some older ppl. they also charge about 20$
webster hall i used to go to a lot back in my early 20s (very crowded) but havent been in a while. i hear that its improved a lot again and a fun spot.
there is also LQ (latin quarter) near midtown. leans toward spanish music but plays a mix of everything. this is a little more *dancy* and an actual club than the other spots. you will find all races in here but if you can dance to a little spanish music you will love this place.
there is more but generally speaking these are your best bets for what your looking for.
2.you dont really have much to worry about. the only thing i can tell you is that you will generally find a younger crowd on weekends and older crowds come out thursday nights. also most decent places get very very crowded so if your all about busting crazy dance moves you wont really have much luck with that. all you need to worry about is your attire and making sure you can get in. sometimes it can be hard for a single guy or group of guys to get into a spot. just remember that the more presentable you look the more you look like you will spend money at the place and not cause trouble you should be fine. this generally just means no street or casual wear. shirt, pants, (or nice jeans) and shoes and def no hats. if the bouncer starts giving you a hard time about ID or something stupid hes probably looking for you to hit him off with a 20$. if your ok with this, have it folded and ready so he can see the denomination and reach out to shake his hand (they know the drill) and say "its just me tonight"
3. dont be intimidated by the scope of things in NYC. the nightlife competition is fierce in NYC and they want you in their clubs.
if your alone, just dont get hammered. never lose control of your faculties on a night out. NYC is much nicer than it used to be but there are very much still predators out there. be friendly and polite but dont be a pushover. trust no one.