Blog site builder understanding

Hello everyone! I'm planning to create two blog sites this year, but am a little confused on how to get started. Looking for some guidance, here are my needs and questions:

I want to create two separate blog sites.

I want them to look professional and unique and may need to use a paid theme.

Should I use WordPress.com or WordPress.org?

Do I need to buy the theme twice for each site? As shown below, you need to recommend hosting services, themes and plugins that are suitable for blogging sites.