I would send out invites if I were you. Like kmk2016 said, you can use it as a pre-information mailer. So you don't have to necessarily have the whole "request your presence" stuff but you can definitely still have a page with all of the wedding information on it.
We didn't bother with STDs, but just sent our invite out to everyone in April/May (100 invites or so). We are planning on sending out passport books with information to the people that have booked in October right after final payments are due. We have all of our wedding and event information info on our website, but we have some older guests coming that aren't as familiar with computers so we want to make sure everyone is on top of things. It'll also be a good way to raise excitement about the trip
I bought the template from Aylee too but I suck at DIY stuff haha. And the thought of putting together and printing all of the passports is a bit daunting to me, so I might just end up ordering them since we'll probably only need about 25 or so. Or if we do budget here, I might just send out a newsletter with all of the information. I want send luggage tags at this point too