https://developers.google.com/season-of-docs/docs/project-ideas says: "Your organization application should include one or more projects that you would like a technical writer to work on."
In Boost, what is considered a project for GSoD? The whole Boost superproject or individual libraries?
Boost is considered the org, projects can have a global scope or be restricted to a particular library.
The page also says: "Once you have selected mentors for your organization, have them register with Season of Docs (...) Organization applications close on April 23 at 20:00 UTC."
Is this period selection of a bunch of potential mentors willing to participate or final mentors who must declare their participation by April 23?
Everyone registered before April 23 is considered potential, final are not chosen until we are acepted, projects are acepted, documentors are accepted, and we assign the mentors to them. However, if you considering to be a mentor, then it is better to register before 23rd.
It looks there is plenty of time to select final mentors, no?
Yeap, I think it is because they don't overlap much with GSOC in case mentors of one want to participate in the other.