There are lots of thread on this. Try doing a search or browse the invite forum.
We sent STDs out about 10 months before the wedding. I would have liked to do it sooner, but that was when we had travel dates, flight info, etc.
Ettiquette-ly (that's my new word of the day) everyone who is told to hold the date should receive an invite.
Since we are having an AHR, we combined the wedding announcement with the AHR invite. I didn't want to do 3 sets of invites (STD, wedding, AHR).