These aren't silly questions at all. There is a learning curve with soapmaking and it takes awhile to absorb just basic info. Let's not discuss variables at this time - we'll get into those later.
Those percentages are good that you listed. In fact, I just recommended those oils at those percentages in a previous post for someone who wanted to do her first batch. It's an easy recipe and produces a nice bar which I consider a basic bath soap.
Since you are new, I'd suggest using the default water amount because it will give you a little more time before trace in case you're not sure of what it looks like. I don't want to insult you if you already know this info. Someone described trace as similar in consistency to a cake batter and when you lift the stickblender to dribble some over the surface, the portion remains on top for a few seconds. Here's a video which shows a good example of trace. (However, I'd never say castile soap is ready in a month. I cure mine for at least 6 months and preferably over a year but this is because I don't like the lather. I also don't make it anymore because I prefer lather with big bubbles.)
[ame]http://www.youtube.com/watch?v=YKBUwV_AbYw[/ame]
1% each of lavender and peppermint is fine. That's about the percentage I use - 2% per pound of oil for some EOs. You could even use slightly more lavender since it's not an irritating oil but please don't go over a total of 3% ppo.
eta: I checked I do use 3% ppo for a batch with lavender and lemongrass. I use it at a 2:1 ratio so twice the amount of lavender than lemongrass. This is because lemongrass is a bit strong and can overpower a blend if too much is used. Disclaimer: This is just my opinion and is based on what I like. Other people may prefer a stronger lemongrass scent.
Again, I don't want to insult you if you already know this info. Superfat or lye discount is basically a fudge factor since SAP values are based on averages of how many mg of lye it takes to saponify 1 gram of fat. It also helps in case scales aren't completely accurate. A 5% superfat (lye discount) means you're using 5% less lye than is required for 100% saponification. 5% of the total oils remain unsaponified - free oils which mostly remain on your skin as an emollient. It depends on what you prefer to use as a superfat and only experimentation in using varied superfats will you find out what is best for your skin.
I started out using 5% superfat combined with 30% coconut oil because this is what I was told would make a nice soap. After a few batches, I realized that it wasn't good for me because it was too drying. It took me several batches to figure out because I thought I was doing something wrong and not an issue with the recipe of too much coconut and not enough of a lye discount. But I have dry skin and for other people this would be perfect for them. I learned to use a higher superfat and less coconut oil. Most of my recipes have a range of 19%-25% coconut with a 7%-8% superfat. When I make soap for a BIL and nephews, I use 5% superfat because it's what they prefer. The values the 50% OO/25% CO/25% PO are in the range of values I like to see when formulating for them.
To condense the ramblings of the previous paragraphs - 5% is fine for some skin types but if you have really dry skin, you might want to change it to 7% or 8%. This is enough of a boost to allow a little more free oil but not enough to suppress the lather. If you can get some castor oil, you could add 5% to your batch since it would help to boost the conditioning a little, increase the bubbles a bit, adds a little creaminess and help to make the lather more stable. I love castor oil and now use it in every recipe. You don't need it to make a lovely soap. Some soapers never use it. But I like what it brings to the party.
My basic recipe for BIL and nephews is the one below with a 5% SF.
45% Olive oil
25% Coconut oil
25% Palm oil
5% Castor oil
