I can totally relate. My shoulder's got so that I couldn't lift my arms straight over my head which I believe came from a combination of my posture at work, (desk and typing for 8hrs a day) and riding 5k a year on my DF bike. (year round commuting). I had seen Lief Z. ride his Cruzbike by me on one of my commutes so I sped up and caught him at the light to ask about his crazy looking bike. Fast forward to last year and I pulled the trigger and am now the proud owner of a S30. I will caution you to spend as much time as you can doing slow speed maneuvers in a safe location (school parking lot on Saturdays etc) as you can before venturing out into traffic. The hardest thing to learn is a cold start on a hill. <rant> traffic planners do not think about bicycles when they lay out streets!</rant> Next find a safe bike trail without any traffic and do some serious mileage on it. Ride your neighborhood streets, with lots of starting and stopping. Practice sprints so that you feel confident at speed. Find a hill without traffic and ride up and down it until you feel 100% comfortable on it. And don't be afraid to walk hills that are too steep. You will find that it's hard to stop going up on a hill that you can't climb (ie your legs are telling you one more stroke and we are so done.) , so quit riding and walk before that happens.
I have been riding for a little over a year and I am not faster than I am on my DF, unless it's downhill. It takes time to develop the skills that I had developed on my DF to cut those precious seconds off at every stop sign and light, to climb as fast as you used to. There are people on this forum who can climb as fast as a DF rider, I am not one of them. I'm not slow, but not being able to stand up and pump every so often means it's tough for me to give my legs a break from the fast spin I need to climb hills here in San Diego. But that's not the reason for riding is it? For most of us, its getting there at all pain free.
And my trick for starting up a hill from a cold start is to stand over the bike, give it a hard shove forward, slide forward and pedal in a quick motion. It's not elegant, but that extra bit of forward momentum gives me a chance to do it at all.
But the time will fly and soon so will you!