Understanding metronic 8 file structures

Hello, after getting this template, I want to use some of its features in my own project. I am using html, css, js, jquery, bootstrap4 with ruby ​​language in my project

1) Can I use only html, css3 and js and features in html demo without scss files?

2) If so, how do the files arrive when purchased? How can I include it in my project?

3) Are there different versions of Metronic? There is no separation on the purchase page.

4)My project is a big project and If there is no css usage in this template, will it be a problem to use the css files in my project as scss? How can I do that?

I don't know the sass structure at all and I don't know what to expect. It seems complicated to me. I hope there is css, but you said that it is not developed, in a comment, the css file that I cannot customize will be a problem for me. If there is a version with html, css and js, can you guarantee that I can use it easily?

5) For example, if I wanted to use only the left menu feature, can I include only its css and js plugins in my project and use it?
After all, I don't want to use the whole template. I want to customize it piece by piece in my own project
Could you please state the way around this clearly?