DOT3 or DOT4. Get a 1L ATE bottle just to be sure. One 1L bottle is enough, I tend to use about half. You usually replace more than capacity anyway, since you might use up extra fluid trying to bleed any air bubbles.
Get a turkey baster and suck up existing brake fluid up to the "MIN" level. Then pour in the new fluid. This will make the process go a bit faster.
While you're at it, you can bleed your clutch, as it's fed from the same reservoir. The only difference w/ the clutch is that when you release it, the pedal doesn't come back up on its own--instead, you have to pick it up off the floor and then pump it back up to normal pressure.
