There is a domain mywebsite.com and for every user i want a domain like user.mywebsite.com
should I buy .mywebsite or .com
Should every sub domain for every user be bought?
how many sub domains can be added?
should I buy .mywebsite or .com
Well, last I checked .com
wasn't for sale, so that leaves you with only one option.
Should every sub domain for every user be bought?
You don't need to purchase subdomains.
how many sub domains can be added?
That's a question for whomever provides DNS resolution for your domain.
You can enable * entries (*.mywebsite.com) for your domain which would allow you to create any kind of prefixed subdomain user1.mywebsite.com, user2.mywebsite.com and you don't need to purchase subdomain for every user. This is supported by domain registrars where you manage your A records.