Seeking Numerical Ratios for Pre-Thinning Acrylics (Hand Painting Only)

I’m looking for strictly numerical, repeatable guidance for pre-thinning acrylic paints for hand painting, not airbrushing.

I’m not asking about color theory or shade matching. This is a process question about volume ratios and storage.

Eyeballing consistency does not work for me. Due to neurological changes from brain surgery, I need measurable steps rather than visual estimation. So advice like “thin until it looks right” unfortunately isn’t usable for me. That's just not how my damaged brain works.

What I’m trying to do:

• Take a 17 ml bottle of acrylic paint

• Add distilled water at a defined ratio

• Transfer/store it in a 30 ml dropper bottle

• Have it ready-to-use for hand painting without remixing every session

My questions:

1. What starting paint:water ratio works reliably for brush painting (e.g., 2:1, 3:1, 1:1, etc.)?

2. Is distilled water alone sufficient for storage, or should a flow improver / retarder be added?

3. Does pre-thinning in bulk cause long-term separation issues?

4. Are there volume calculations I should consider when scaling from 17 ml to 30 ml?

I’m specifically looking for concrete numbers and repeatable methods.

Thanks in advance to anyone willing to share practical experience, as people local to me have been unable to understand my cognitive limitations.