If you are stressed out about wedding stuff, remember:
--you have 6 months to activate the visa
--you can do as others have suggested and do the civil wedding first, big frou-frou wedding later
--you can start planning now!

What Jerry and I did was make all the decisions ahead of time and have everything set to go, so once we had a good idea of when we could have our wedding, we just set things in motion. Oh, and we did something then (which we could kind of get away with then) that I wouldn't reccommend doing now -- we set the wedding date before I had my visa in hand.

And we scaled way back on what we wanted our wedding to be like -- instead of having tons of people and worrying about catering and all that kind of stuff, we focused on having a special intimate wedding at an amazing location with a few family and friends on that day, and we had a couple big parties for everyone else later. It was wonderful.
Based on my experience, these are my two biggest pieces of advice:
--go to your wedding vendors ahead of time and explain the situation you are in, and see how flexible they can be. Our wedding/reception site and the that da photographer/videography team were fantastic and were willing to work with us in case of delay and such, within limits. Because we were willing to be married on an "off day", this helped even more.
--cut out as many middle men (ie. wedding vendors) as you can, and do as much of the wedding yourself as you can. That way you have less people and deposits to worry about if something happens while your visa is processing.
Our wedding may not have been at the spot I always imagined it, but it turned out to be perfect and exactly what we wanted it to be.