how much
I am still a novice about making soap. Unless you melt your own fats (bacon, tallow, etc) your soap should not spoil. Spoilage can happen when there is little bits of meat left in your fat (from frying it or melting it down to use for soap) that get into your soap if you didn't filter it out first. I have had soap sitting around for 3-4 years, and it's still good. As far as using Oatmeal, just don't use "quick-oats" or instant oatmeal. It can clump up on you, use the slow cooking or "old fashioned" oatmeal, and grind it up in a food processor first and add it last to your soap before you are ready to pour it into your mold..
I sell some of my soap to my customers (I'm a waitress) but mainly use the soap for my family. I don't use goat milk or oatmeal, just lard and or vegetable shortening, olive oil, palm oil, coconut oil, sunflower seed oil. I switch sunflower seed oil with grape seed oil, etc. I use Olive oil cause it cause's the soap to suds up. You don't need suds to get clean, it's more psychological than anything. I also let my soap dry really well - a dry bar of soap lasts longer (even with store bought, unwrap it and let it dry more before using). I store mine unwrapped. I leave mine on an open-grate shelf. I make about 36 4 1/2 oz. bars at one time. That's what size box (it was an old dresser sock drawer) I use as my mold. I think it measures 14"x12". My soap is usually ready in about 2-3 weeks after making it, and I always test it by washing my hands first with it. If your hands rinse off squeaky clean, it's ready. If you hands rinse off and they are still slippery (like when you have bleach on your hands) it is not ready - give it another week or so and try washing your hands with it again.
My first book I bought on soap making is called "The Complete Soapmaker".
http://www.amazon.com/Complete-Soapmake ... 0806948698 I really liked it. It is very helpful. It's on amazon for $4.46 new (a lot less than what I paid for it years ago). I have another book I also use but I can't find it nor can I remember it's name. I use it more than the above mentioned, only cause it make a smaller amount of soap (not by much though) in the recipe's she gives. These books will give you weights and amounts of fat and lye/water to use, so the hard work is done for you. Once you see how easy it is, you can do some experimenting on your own with different fats (as long as they add up to the same total amount in the recipe). Like if one recipe calls for 8 oz of palm oil, I may use 10 and then cut back those 2 extra oz. on another oil..AND, I
never alter from the lye amounts (or the water for the lye) in these recipes - I haven't figured that part out yet, and am very happy with the results in the books I read.
I bought a digital scale at Wal-mart, too. Fat and Lye (even the water for the lye) should be "weighed" and not measured. 6 oz. of fat in a measuring glass can be different than 6 oz. on a scale. I didn't spend a lot on the scale, and it does the job. No use going in debt if you don't have to.
I hope I have given you some help. Enjoy making it, I look forward to when my supply gets low and I have to make it again. It's like a fun science experiment that always works out. I want to hear how your soap turned out, how well you enjoyed doing it, etc. Good Luck!