I have OSS, but it still took me a month to get really used to my bike. I can keep pretty stable now at down to 4 mph, but below that I definitely have problems. Part of it is practice -- I just don't go that slow, except when I'm coming to a stop.
As for starting, part of it's gearing down properly, and part of it's muscle memory and strength. When I first started, even when I geared down, I had a hard time, just because a) I didn't have enough power for a good push off, and b) I couldn't clip in fast enough. And starting off going up on a hill was terrifying. But that's all in the past.
Give it some time and practice -- you'll get there!
I routinely go on roads where the cars go 60 mph, but where I ride, people are used to bikes. That makes a big difference.