How many letters in the title of Chapter

good afternoon
In terms of search engine more accurately matching the material to the title as it is told, the better.
You are in a tutorial usually write fairly small headlines - and it looks nice)
learn.getgrav.org/basics/what-is-grav
but I am a lawyer, and a typical header looks like this - "the basic rules of the marriage contract in New Zealand law."
So I wanted to ask - How many letters can contain the article title?
and
Can I make the header is printed in two lines - not to make the menu half the size of the monitor screen
Thank you

It all really depends on the theme you are using. There is no hard-limit on the number of characters. You just need to ensure the theme + CSS allows long titles to wrap properly and look ok. It's not really a Grav thing, its a just a web/html thing.