Thanks for your question, and welcome to the world of WordPress. Many people here may say this isn’t the right question for this site, but I think it’s a great one!
There’s really no perfect way to do WordPress, and almost always there are a lot of options to do it right or well.
Categories can be important for SEO and they can be a great tool, but don’t get hung up about this. As long as you have good content, and real humans can navigate your site, you should be satisfying the basics of SEO in terms of your site’s structure.
The question of ‘how’ you should do this really comes down to your personal choice, and also that of the theme or template you’re working with (or building if you’re here to build things yourself!)
Perhaps make sure you’re testing how things change when you add content and new pages. From the information you’ve given, I’d probably suggest you do these as child pages rather than categories, since child pages will give you better control over your ‘flow’ and ‘page order’ whereas categories will normally order themselves alphabetically.
See how you go and I hope things work out for you!