Office 365 Shared Mailbox in Exchange Admin

I am creating shared mailboxes in my Office 365 account and I want all the users on my domain to have access to all of the mailboxes. Is there any way I can set this up automatically, instead of manually adding each user to each shared mailbox and then having to remember to add all new users into each shared mailbox?

Also is there anyway I can only allow them to have View-Only permissions on these mailboxes?

Thanks