What terms do I back link to my home page of my site in the publication of links guest post on big and valid sites?
Can we use our site brand as a keyword? For example, "google" word for address "www.google.com".
Anchor text isn't really a thing in 2018 so I wouldn't worry about it. The risk is you can over optimise.
As long as your homepage ranks for your brand (which it will as long as you don't over optimise by having loads of exact match anchor text) then you'll be fine.