Several other aspects other than audience size will determine what you will need to spec. Criteria such as # of vocalists, #of live percussion/drum mics, # of other instruments and their types(direct or mic'd),other sources(DJ, groove boxes, etc), all will factor into what you need to spec. That will also determine the console size, the snake configuration, and monitor configuration.
Audience size will mainly determine what the speaker/amp arrangements will need to be...Not to mention that the accoustics of 1 venue of 500 can be very different from another 500-seater, and that will also dictate what you need to have onhand. Hip-hop does require some serious subwoofer activity and that will need to be addressed as well.
Stage volume levels that the band generates will also determine what the monitors and house systems will need to meet. You might check with a local sound company familiar with the venues that you are planning to use to get an idea of what is involved to produce your desired results.

(More, sorry) I recently did a hip-hop gig for a fundraiser, in a Hilton ballroom with about 700 people coming in and out all evening. I maxed out a pair of Allen&Heath GL2200s at FOH (48 channels), and a 32-channel Hill Multimix monitor board. (2)DJs, a pair of multi-keyboardists, bass, guitar, (2) percussion rigs, a full drum kit, (4) vocalists (wireless, and 1 also played alto sax with a wireless on that)...it adds up in hurry. The house was (8x) dual-18" subs (4/side), (8x) TAD-loaded PAS T.O.C. boxes, (4) PAS line arrays as frontfills, (8x) JBL-loaded floor wedges, and a couple of sidefills for each keyboardist. Crown Microtechs for all. Not to mention EQ, comps, DSP, DIs, blah, blah, blah...it never really ends, does it?

thanks...but is there any basic place i can start? any basic needs? i know it hinges on several things but i just need to know at least general specs to start with...

One great way to get the info you need is to call a rental or sound reinforcement place and ask them, they'll usually have that info handy if not on their site. 8-)

From the info in moonbaby's last post, there are a lot of variables. Hip Hop groups can rage anywhere from 2 turntables and a microphone to a full band including percussion and horns...possibly background singers.
So you can see why we can't really give you specifics.

But...you wanna place to start...here:

mixer, mic & PA

24 channel board
1 dozen or so mics, get a couple of wireless ones for the MCs
mic & instrument cables...LOTS of 'em
24 channel snake w/stage box
Adapters/DI Boxes for them turntables and other non-XLR stuffs
Outboard gear, Gates, Comps, Efx, etc.
PA system including, power amps, speakers, subs, monitors, cables, - Really depends on size of venue

You could always get fewer channels. The average hip hop artist doesn't have a full band and probably only needs a couple mics and a couple channels for audio. So you might be able to get away with an 8 channel mixer.

That's awesome advice also with hip hop it's good to find out how the artists will be presenting their backing tracks. Some guys bring a live deejay, some guys just show up with a CD. If you aren't sure then definitely have a reliable CD player in your rack just in case. 8-)