ive been riding fixed gear for over a year and im about to acquire my first road frame. the frame is what i believe to be a 1998 cannondale saeco r4000. the only drivetrain component it comes with is a front derailleur. now i know im going to need a rear derailleur, brakes, wheels, and shifters but where do you start?

i was looking at entry level components such as tiagra and sora but if anyone could point me in the right direction that would be great. i plan on just getting the bike running for summer and slowly upgrading. how do i know what derailleur to buy? anyone know where to find cheap (relatively) shifter/brake levers online? this whole geared thing has my head spinning. i know some people would say to go and get a new bike but i really want to learn the whole geared bike thing. thanks!