I make cold process soap, and for starters the fat used determines how much lye you need. You cannot use the same amounts lye and fat for whatever fat or mix of you have. There are calculators for such online :
http://soapcalc.net/calc/SoapCalcWP.asp
Otherwise, yes use more fat then the lye needs i.e. oversaturation, 3-5% is normal for some mosturizing and the safety that all the lye has found some fat to join with. You can use fairly limited amount of water (less shrinkage of soap during curing process), but fat and lye are the chemical reaction here, the water just helps things come together.
There are people that make the lye even, (running water through woodash), but that is a hit or mis thing strength wise and if you want bars of soap that need to cure, are way milder on your hands and can be stored you'll need to add salt to the mix. The lye you can now buy for soap making is sodiumhydroxide (sodium being the salt). So total number of ingredients in barsoap is 4 (water, lye, salt, fat).
I use just oliveoil because i can easily get it and i started making soap to replace the alleppo soap that while good was both expensive and awkward to handle. Now with individual molds the soaps are both pretty and invite handling and thus use (and that is what they are for).
While i would like having volume measurements for soap, i don't want to risk it, i make it for myself and a few family members like a few small batches every 2 years or so. Experimenting is fun, but i cannot test for safety well enough other then just use it to want to mess with alternative ways of portioning the ingredients. Adding some coffee grounds is a good addition for getting hands clean after gardening and such and it looks like a tsp of honey is good also, but other amounts go by weight to the gram.
