Subscribe, Font changes a few more

Much appreciate if you can guide me through the following. I had a custom theme that is not working with the new PHP versions, hence from now thought of sticking with WordPress default themes. Moved to Twenty-Twenty. I need a few basic features added, can you help?

1. I need a way for individuals to sign up for my blog so that they can get newsletters/weekly writings. Is there a way I can add this to the side of the front/home page? A sign-up box for them to provide email, name, phone number?
1 a. Is there a way to add text on the side to describe what the blog is about, like a one-paragraph simple text box?
2. How do I change the font size of the post headers on the front/home page?
3. Instead of my post content being align left, right or center, is there a way I can have an align-justify?
4. I want to put a header image for my blog site so that it shows up on all pages, what is the best way to do it? similar to any other site, like the one you see for this site wordpress.org
5. I don’t know how to use this block writing feature, I will search for some tutorials if you have any suggestions, can you share?

Thank you for your help.