The online AADSAS application will be released May 15th, however you can look at the current one to get an idea of what is required, since it is doubtful that the form will change much, if at all. AADSAS apps. may be submitted beginning June 1.
Send in your DAT registration info, and they'll send you back a confirmation letter with instructions on how to contact the Sylvan center. Once you have that letter, you can register for the test for one year, so you might as well send in the info when you have a fair idea of what schools you are applying to.
ADA only took 2 weeks to get the confirmation letter for the DAT back to me, but with the busy season coming up, I've heard that it may take up to 6 weeks total, so be prepared for that. Best to mail in the DAT app. early and then secure your preferred testing date.