Yes, the mini Digibase kit only makes 250ml of stabilizer. Yes, you'll have to hold the tank horizontally and roll it. I set it in the floor and roll it with my foot.

No, do not add Photo-Flo to the stabilizer. The stabilizer should be the last liquid that touches the film. If you do a distilled water rinse, do it after the post-fixing wash, and do the stabilizer last.

And yes, the stabilizer will last for many, many rolls of film -- at least as long as the bleach and fix.