Some question about customizing

Hi! No need to say that I love your theme but now I want to customize some parts. Sorry if I make so many questions but here we go!
If you need it, here’s my site: https://www.ladypingu.com

1. I want to make bigger the part where the entries are posted but keeping the right sidebar in the size it is at this moment. (Width of the main body)

2. Is any way to add a header to the page below the main menu?

3. Can I make bigger the title of the blog?

4. Can I make bigger the title of the posts, make smaller and change the typo of the main text?

Thank you so much for your help!!