Currently no, but in the next major release on the platform (due within 2020) you will be able to ‘favourite’ brands and get notified when there in an opportunity posted by any brands that you ‘favourite’.
No, you will only be notified whether your application was successful or not. You will be advised and subsequently informed if the Brand has shortlisted you and their final decision, but no further feedback will be given.
A good bio is one that contains as much informative data as possible to ensure you are attractive to brands, yet also tells your story in a compelling way. Include as much information as you want, and feel free to supplement this with videos (upload directly or link in from YouTube), and links to articles. You should also connect up your social media accounts if you have them as some brands take number of followers into consideration.
Yes, this can be done in the description of the opportunity or it can be discussed directly with the talent via the messenger within the platform. Please note also some talent may have some restrictions of their own due to sponsorship arrangements.