If you go with water based paint, dilute the first coat about 50% with water, this will allow it to penetrate more and it will act like a sealer. Then put on a second coat. Avoid flat paint, they fill it too much and the inexpensive stuff is poor quality. I would go with a gloss or semigloss as it contains more polymer and will seal/protect better. It is also easier to wash and picks up dirt less. Do not use an interior paint for exterior (or vice versa) or you are asking for problems.
any water borne paint will allow the wood tannins in the OSB to leach through the paint. Your white will be yellow. You need to paint it first w/ an oil based primer. one coat of oil based primer and one coat of 10.00/gallon barn paint will look 10 times better than 2,3,4 coats of expensive white latex paint. Original Kilz oil base is a good, cheap way to go.