who knows about where to use latex house paint?

[Salty]

The flat latex you have can be used as a primer on raw sheetrock because the vinyl primer that is formulated for priming is basically a lower-end acrylic flat designed to keep the sheetrock from absorbing the finish. Very little "priming" involved.

As far as using your paint inside....it's perfectly fine. Folks don't use flat/matte finish anymore, tho. Even on ceilings they use satin...mostly because it brings out the texture on a skip troweled ceiling. On walls and trim, the satin is able to be wiped...flat, not so much. You'll actually wipe the paint off the surface tryin' to clean it. The reason the moisture shows on satin/semi-gloss walls in bathrooms is because the paint is blocking it from soaking into the sheetrock. Flat paint in a bathroom is NOT a good idea. It's prolly more porous than the sheetrock, itself. It will eventually begin to peel.

Good luck and holler at me if you have any questions and, remember...paint is only as good as the surface you put it on.