technicaly you need 8:4 ratio of sand to lime for your lime coats (upto arriccio)and 8:5 for intonaco (painting plaster layer). On a Small panel and/or tile used for practice purposes you can skip scratch (base rough lime/sand/cement layer) and start with arriccio+intonaco

for the ease of experiment/learning stucco a section of the wall 4X8 or so feet leaving it really rough:

see "Albuquerque Fresco" topic for some pics of a scratch coat:
http://www.truefresco.com/albuquerque/preparation_albuq.html

This will help you to practice applying plaster and what not, you can scrape it each day and start new untill you are ready to move on.

>...so I try 1/4 cup variations in the water, weight >the lime in a scale like I would a glaze.

not clear on what do you mean here...

After you have turned your dry (for practice you can use any lime including the one sold in home depot) lime into a paste - of a heavy sour cream consistency take 4 cups of it and mix with 8 cups of dry sand - this will be your arriccio. For intonaco you will need 5 cups of lime to 8 cups of Fine (sifted through window screen) sand. You DO NOT need to add water it will be just enough in the lime putty. Use what's called "Plaster Sand" for your plaster home depot or masonry yard sells it, NO SILICA SAND. Prepare your mixes day before use.
(directions in "how to make lime putty" topic in Cafe al Fresco)

If you have the "scratch wall" prepared than soack it in the evening with water and in the morning it should be ready to receive plaster without additional soaking - it should have a consistent wet-gray color, if there are dry-looking (lighter gray color) patches than you did not soak it enough the night before - if there are not too big you can perhaps mist from the spritzer bottle undil they dissappear and do not come back in 20-30 min.

No you can apply your arriccio - you should not need to add water to the mix you have prepared but you need to "rework it" before applying, it is allowed to add just a little of a lime water to make the mix a bit softer - a little > for 1/2 of 5 gallon bucket of plaster 1/2 of a small cup of lime water... do the math for smaller ammounts of plaster.