Hi all - sort of new to this board. Appreciate all advice

Wedding is July 16, 2011:
1) Should I send STDs?
2) If so when?
3) If no STDs, when is the soonest I can send the invites?
4) Is early March too early to send invites?
I have noticed that people think sending invites too soon is bad etiquette, I am just wondering why. What is the problem with that? I am not sure so that's why I'm asking. Thanks!
BFP#1 10/17/11, m/c due to SCH 11/21/11 @ 8w4d; BFP#2 2/26/12 - EDD 11/4/12