Soapmaking lather question?
Sorry, I only read the firs repost haha! As the guy above says, stearin acid content should be high for what your after. Clays can be tricky, it's pretty much a matter of trial and error with them. If I were you I would do a very small batch to test your recipe, and keep making small batches and tweaking the ingredients until you get a product that you like. Also keep a note book and write down everything that you do for reference.
Soapmaking lather question?
I have never bought steric acid for soap so I can't really comment, stearic acid content is made from the saponification process of fats, and fats like tallow as said above have a high content, which is enough in my opinion that you shouldn't have to add any extra.
Also glycerin is good, but again when a fat like tallow is saponified, up to %25 of the final product is glycerin so you shouldn't have to add any. Mass produced soaps have the glycerin removed and sold as a by product, but in your own soap the content is very high compared to a soap in a shop.
Soapmaking lather question?
Also with your lye solution, you will want about %5 to %10 less sodium hydroxide then fats, so that there is a portion of super fats lefts over from the process that have not been saponified. A soap where %100 percent of the fats have been saponified is too harsh and only suited for laundry soap.
Soapmaking lather question?
As I have never added stearic acid to any soaps I have made, I don't know and cant really comment on it. I'f it was me Id just make a small batch to test It with a very small amount. You would have to talk to someone who has successfully made shaving soaps and has used stearic acid. I've done a couple of batches of shaving soap, but the results left allot to desire and I didn't bother perusing It any further. All the experience I have is with bath soaps and hand soaps, lotions and moisturisers.