Yes, unless you were to use sub domains . If you wanted to promote different niches then separate websites would be best.

Not necessarily Subdomain on Your Own Dot Com Website

Yes , but choose the domain name wisely , you can not change it in future.

Yes as this is your websites address, so you will need to direct people to different places if you have different websites

A domain is a website. So if you want 5 different websites then you need 5 different domains.