Erp a derp, I didn't read thoroughly enough through your questions... I answered for Sodium Acetate, not sodium lactate... I may be back with info that I find, if any...
Here we go...
"Sodium lactate is a natural humectant, moisturizer and pH regulator. For lotions replace the liquid glycerin with sodium lactate, in soaps use up to 1/2 ounce per lb of fats to harden the bar. Produced from renewable resources and completely biodegradable makes sodium lactate a better choice when moisturization is desired. Studies have shown sodium lactate to be a better short term and long term moisturizer than glycerin, our long loved friend. Try the tests for yourself.
Make your favorite lotion twice, once with glycerin and once with sodium lactate. Apply the lotion to your leg or arm twice daily for 2 weeks. We are sure you will notice the difference. Sodium lactate is less sticky when compared to liquid glycerin so if you are trying to formulate to make a less sticky lotion use sodium lactate instead of glycerin. Sodium lactate 60% USP."
Above information was found here:
http://www.soapgoods.com/Sodium-Lactate-60--p-1440.htmlSo, as for your questions, I can answer the first one:
1) Dosage 1%-3% - that's ok?
The above paragraphs say that it's ok to use up to 1/2 ounce per lb of fats which works out to be 3% max usage.
I think Soapbuddy can answer the rest of your questions though as I believe she's used SL 60% in her soaps, too.
Good luck!