To stress or to calm down? I'd say yes and no:
1. When I was first engaged, it seemed that I had so many important decisions to make RIGHT NOW! The date, the location, the wedding attendants . . . but once those very important things were chosen, I didn't have all that much to do until about two months before the wedding. So don't confuse these initial choices (which are legitimately stressful) with what the next 9 months will be like!
2. Decide now on your priority items. Do you care tremendously about the dress, but the music isn't all that important to you? Or do you want a blow-out reception but consider the invitations a blow-off item? Decide now what items mean most to you, and put your efforts into those things. Pick out the 3-5 things that are absolute must-haves, and go all-out on those things . . . but be moderate in everything else. So if photographs are super-important to you, put in the time researching your options and put your budget into that . . . but then accept that you have little time and effort for the cake. The point, of course, is that you can't make everything a top priority, so decide what matters to you.
3. Once you make a decision, let it go. Don't continue to re-hash it in your mind, don't continue to comparison shop, don't worry yourself ragged about whether a better option is out there. Don't lay awake at night wondering if you should've chosen a 5-tier cake instead of 4-tier. Don't second-guess your flower girl's dress. Make a choice, and move on to the next one.
4. Seek a healthy balance between "this is my one and only wedding" and "it's only one day in your whole life". If at any point you're over-stressed, take a couple days off from wedding stuff. But accomplish as much as you can within the next months; don't leave too much for the end. And along with this, accept that something will go wrong, but the point is to be married in the end -- not to have a perfect party.