As far as standing while coasting, I do that sometimes for visibility, I regularly ride a big hill with a hard-to-see intersection, standing a bit lets me have a clear view of any cars.

I had the same exact problem when I first got back on a bike. I found that the standing thing came naturally as I got more comfortable with the bike. At first I was really frustrated that I couldn't do it. I could do it in Jr. High, after all, on my parents old 10 speeds that fit me miserably. So I had my LBS look at the fit on my bike again, all good, I was just a turkey. But then one day I just stood and jammed up a little hill without even thinking about it. Once I was comfortable on the bike it was all good.

As far as clipping out at a stop, I usually ride in bike lanes and one thing that I love to do is to ride up next to a curb/ped x-ing sign etc. and use that as a rest for my right foot. That way I can stay in the saddle and keep my left foot ready to go when the light changes. I found that the thing that helped me get good at stopping and unclipping was learning to maintain my balance while riding very slow.

BTW, I usually ride a mountain bike. I just got a road bike and am a total klutz on it. I figure that sooner or later it I will feel as comfortable on it as I do on my MTB.

Good luck!

Anne