Domains differ from hosting, so both are required. Domain registration gives you the ability to point a URL towards something hosted on the internet. Hosting is needed to have content available online that your URL can point to.
Yes, unless you want to forward your domain to the webflow.io domain (which includes the Made in Webflow badge).
In your example case, you should really only be paying ~$10-15/year for a domain (I’d guess their $5/month plan includes some form of hosting - which isn’t necessary) but otherwise that’s accurate.
Your English is great by the way, no need for an apology. Let me know if you have any other questions.