Hello! The general consensus is using bar soap as shampoo is bad for your hair, as it is too harsh. Some people have great results over the span of a few weeks, but the damage eventually catches up. Some people with strong hair may have better luck, but most aren't really willing to take the chance.
Soaping is a super fun hobby, and you're right, the only testers will be you, your friends and your family. And it always feels great to make something yourself, right?
There is definitely a lot to learn before you even think about making your first batch!
The recipe on the website you posted isn't a good starting point. You can actually formulate your very own recipe for your first batch and keep it very, very simple.
Reading about oil properties can help you understand what the different oils bring to your soap. Some produce a hard bar, others effect lather, creaminess, bubbliness... there's a ton of possibilities.
When coming up with your first recipe, we generally use percentages/weight instead of volume, for more accuracy and ease of sizing. Digital kitchen scales are very important.
Here are a few things to start your research:
1. Read about safety! You will need gloves, goggles, a long-sleeved shirt and special safety precautions when working with lye.
2. Read about oil properties! Find out which oils are available to you and what basic oils are important for a bar of soap.
3. Formulate your recipe! Find some beginner recipes here on the forum that sound good to you. Keep it simple! 3-4 different oils is all you need. No fragrances or colours yet. Learn about things like lye concentration, superfatting, temperatures, SoapCalc.
4. Post your recipe here for feedback before you make your first batch. Tweak as needed.
5. Make your first batch, woohoo!
6. If all goes well, in 4-6 weeks you'll have your first soap ready to use.