Will Disney allow an author to write a book that is part of the legends since the new cannon is out? I realise you'd need to be an established author to do so, but i wondered if anyone could add to star wars legends.
Yes, Disney will commission authors to write more books in the Star Wars universe. The Star Wars franchise is extremely successful, and as long as it remains so there will be more media related to it. We do not know for certain if there will be Star Wars Legends books, but there appears to be some information that "[n]ew books will not be labeled Legends, but it is possible that material from Legends ... will be introduced into canon".
Yes, Disney commissions only experienced writers. Some began as writers of fanfiction, but as Mercedes Lackey has explained on Quora, "writing a licensed Star Wars novel ... will not happen unless and until you have a good enough reputation as a professional writer that Disney approaches your agent with an offer. Neither Lucas nor Disney ever hire someone without a good, solid, portfolio of solidly-selling books behind him."
No, you cannot make money writing Star Wars books, unless you have been allowed by the copyright owner to do so. Star Wars and its characters, spaceships, and so on are either copyrighted or trademarked, and making money using those copyrighted stories or trademarked items is a breach of the law.
As an friendly advise: This question should be asked to Disney instead on WE. I doubt here is someone, who works for Disney and can tell it. The only thing you can do is try call them and ask them this question.
It is everything you can and should do.