We're sending STDs 1 year in advance (so, in just a few days - I'm super excited about it!). We only have a small number of them going out, about 20, so perhaps they're not absolutely needed, but rather than friends calling us or taking (incorrect) guesses as to when we said our wedding was, I'd rather they have a magnet on their fridge with the date and location on it. With guests scattered across multiple states, countries, and continents, STDs just make sense for us. I did DIY mine to save money.
We haven't settled on an exact timeline for the rest yet. I'm thinking about sending invites around the 4 month mark. I feel like with our small guest list, all close friends we talk to on a regular basis, we can reasonably expect people to know by that point if they can come. We'll be giving them a month or two to RSVP. If we give them 2 months, that would give us a head count 2 months from the wedding day. I feel that is enough time to finalize things, although it sounds scary, compared to traditional timelines. I do expect most our friends will let us know sooner, though. We've already had some ask if they can book airfare and a room this early. (Ah, tax refund season! If only we were getting one!)