Regarding your first question, every oil requires a different amount of lye for saponification. So there's no way to answer your question unless you specify which oils you will be using and in what proportions.
And on your second question, yes, to reiterate, keep lye out of reach of children and pets. Use safety goggles, gloves and protective clothing when handling it. Do your research. Do you have a plan to deal with spills? Burns? Or, perish the thought, if somebody ingested it by mistake? Do you know what kind of container to mix it in? How to dispose of lye properly should it be necessary?