Custom Theme not loading
Have you looked at the folder structure that the preinstalled core themes have, or have you tried to download any free theme and looked into the folder structure? Have you seen to it that all necessary files are present?
It could even be easier to start with an existing theme and just customize the CSS to fit your needs. I always do that. Look at free themes and find one where the page elements like header, navigation, footer etc. are similar to your layout and go into the theme's main.css and typography.css to edit the theme
Now I have your files I can see why you are struggling..
In the UK it is now 23:00 hours and I need to sleep,
In the morning I will work on this for you and get in touch when I have something for you to work with..
Even if I get this template uploaded as a theme I still need to create the other pages. It's like every time I think I moving forward on this project, I go back to the beginning. Ugh!
I will leave it to you to do that..