Bonsai soil must be free draining. Lots of folks are using Napa autoparts oil dry. Pn 8822. Thats where I would start. Also a bigger pot means more roots, and faster trunk growth. You might like using a colander instead of a pot. There are mixed opinions about them, but for my bougies theyre working great, and cant be overwatered. There are threads about soil and colanders, where many of your questions will be answered. Soil for bonsai is like pasta sauce, everyone has their way of mixing it and opinions. But the 8822 with a little organics mixed in is a good place to start. Even 20% potting soil will work for organics, you just want a little water retention. Read about parched water and how it works in little shallow pots. Learning watering and having the right soil are the two things you should study up on. They are very important, and need to be learned first IMHO. Im kinda new to bonsai and can tell you those are common advice that we all agree on. Even if we dont agree on the soils make up, I think we all agree that its very important. Like live bonsai or dead bonsai. I hope that helps. And welcome to the nut. Bring alligator thick skin, read a lot, and you'll fit right in..