Fake Punk Fan
the only advice I would give you is start booking shows as soon as you can and make sure they go off well (ie: promote them, don't say you'll pay guarantees you can't afford, get someone to make you good looking flyers/posters). After doing this enough, you'll have the relationships with venues you need to be able to call yourself a booking agency.
but this whole business is run on reputation, so you really need to work on booking solid shows first before you even begin to think about being an agency. If one person fucks up a show they booked, oh well, most people will say they learned from it and will book better shows in the future. if a "booking agency" fucks up, people will say "fuck that place, they suck" and not want to work with you anymore.