Like anything in life the process varies.
Schools will begin reading your apps the end of June or so. One TX school doesn't even send out secondary invitations until the end of June.
They will read the complete ones first and read others as files become complete.
Interview
invitations begin in July at some schools and August at others, and end in January at some schools and February at others.
If you'd like to see how things rolled out last year, check this post:
#2
I'll say this for the first time the application season:
Being the first is not important. Interview season spans 7-8 months.