Hey Benjamin,
do not worry, First of all, you did a great job already and now I even know who you are (movie addict here and I recognized some of your work).
Can not wait to see the finished site to read more about your work 
You did a very amazing job already on your website. Great idea setting this all up like you did and impressive vision for somebody who says its not their skill set.
I recommend starting like this:
Clear your formatting for each text using the “clear format” button in the text editor.
Because they overwrite the global settings in simple words.
Set yourself a structure for the different headlines H1-H6 as well as text.
Start with the desktop. Define which H should have which size and color. Be aware about this
If you want to dive deeper into this → Header Tags: A Simple (But Complete) Guide To H1, H2 and H3 Tags
Then, when you think your text, headline and all look great on Desktop, switch over to Tablet and then Mobile.
You will see different coloring on the viewports. They will be reflected on the fields like font-size etc. as well. More on this here: https://help.sitejet.io/hc/en-us/articles/24275878741015-Responsiveness
Stick to your plan and check this then for Tablet and Mobile view.
As @Barbara_Bichler said, this is one good way - go with REM for mobile and see for yourself. You can always check your website on your own phone directly via the Preview Link.
If you think you need to format a certain part of the text differently do it in your text editor. But, keep it simple. 
Oh and how you managed the /home images with the buttons to the right section of the subpages is amazing. Good work!