I don't think I'd be interested in one of the less expensive synthetic saddles. For one I'll be living in the desert and I think that leather would hold up better than synthetic in the heat (though I could be wrong about this). For another: personal preference.
As for bridles, would I need different bridles and types of bits? Are the noseband and martingale requirements different for each discipline?
If there is an online resourse that answeres all these questions feel free to direct me there rather than taking the time to answer all my q's! I'd just feel better showing up to an eventing barn with some knowledge under my belt rather than having to rely on my instructor to teach me all the "little" things!