Can i just buy a domain and hosting then apply for the program and get accepted straight away or do i have to have content on my site first?
Content is necessary, why would they accept a blank site that isn't helpful to their potential buyers? I also think you need 500+ monthly visitors, so 25 daily should do.
Content is necessary and content is the king of your site. Without content, there is no way left for you to attract traffic.
Build your site first. Get some pages written. Have your site have at least 5 pages. And do it with quality. Then ask for an amazon account.