I like to use the silk amino acids and the soy in mine. I also add panthenol pro-vitamin B5.
Another good site for ingredients is
http://www.makingcosmetics.com/
Two weeks is about right for storing FSG in the fridge. If you find you cant finish up your batch within two weeks, some of the ladies here freeze portions of theirs. I haven't personally tried that. My daughter also uses my FSG so we go through the stuff pretty fast. But, if I was going to freeze some I'd probably freeze it before I added my extras. Just plain gel with mag sulfate. Then add my extras to the defrosted gel when I was ready to use that next batch.