Hello @shmulik77,
The plugins depend on your requirements. For most people Tutor LMS and WooCommerce is enough and some people install upto 63 plugins on their website.
If you need something minimal, then you can start with a free theme and use a page builder to design things. If you are short on time and need something fancy, you can buy any of our themes. Especially, Skillate is a very nice theme and has mobile friendly design.
To use Tutor LMS, you need to know nothing extra. As you have already created an account here and posted a question, I believe you’re good enough to use any software.
If you want to customize, then you need to know PHP, WordPress functions, actions, filters, hooks etc.