Sounds like you have the fire in your soul - not just the brush!

I really like the idea how you have adapted fresco to your local circumstance and materials. It would be easy for me to point out that 'sharp' sand is preferable to 'rounded' river and beach sand. But you know - the use of local sand, from the local river, may just increase the demand (and price) of your work! If you insist on washing, I think because it is not sea water, with salt, the point of it is screen out tiny particles/dirt - so you need a mesh screen of some type. The sand and gravel companies use this all the time - but of course their needs, and volumes are entirely different. Try a garden supply - they screen soil too. Maybe leevalley.com

That is an annoying stage when you are all set up to paint but the lime is still too wet - I have put a hair dryer on it in the past. Don't forget I also overpaint with potassium silicate and fresco pigments - slightly moisten the 'green' lime (say within 24 hours of it setting off) and it paints exactly like the 'golden' time and dries matte too. This is as weather resistant as lime fresco. The only caveat is that if it does build up to thick (multiple layers of silicate) it may shine a little bit so it really is best for touchups, line work. A lot less stress anyways.

Lime compatibility you can check yourself or go to kremer-pigmente.com. They sell small quantities of potassium silicate too.