0%
This is your own online school, the home where your students will learn. Build it out, tick each step off, then invite your current students in. You can start teaching the same week.
Start on the $9 Hobby plan. It lets you take payments and run paid courses (Skool takes a 10% fee on sales), and it is all you need to run your online tutoring business, no problem at all. Later, if you want to grow your business more formally, you can consider (not must) upgrading to Pro ($99). Its main draw is the affiliate program: every student in your community can help spread the word, and they get a little perk for doing so. It is not that Hobby cannot grow, Pro just makes it easier.