It's never to early to send Save the Date the cards as destination Weddings take a lot of time to plan you should mail them out as early as you select your venue and date. We think 9-12 is a great idea!
Guests will need to coordinate their travel plans as early as possible, so we think it's important to include the wedding date and location in addition to a link to your wedding website for details on travel their travel arrangements. It's important to keep it simple and informative so they understand if their is a RVSP deadline and your travel agents contact information.
The choice is yours, but we feel it's important to send out both, since a card can get thrown away and the goal is to get a good turn out for your celebration you need to cover all bases. A E-card will have a link to your website since they are already online, it will make things easy, you just want to make sure you understand your guests. Is everyone on your guest list tech savy or those without email access (ie grand parents)?
A good rule of thumb is to send everyone both a "save the date card" and "formal invitation" to your destination Wedding.. even they reply "no" to your save the date card. Since planning a Destination Wedding starts early (12+ months out) you never know if plans change after they see your beautiful Destination Wedding Invitation... they may change their mind and go! It's always a good common practice to include everyone for your invitations and save the date cards.