I just wanted to say I think you're doing the right thing by taking a course or otherwise learning to use a drysuit before arriving in Iceland. From what I've read, dive ops there will take divers who have never used a drysuit, give them a short course, and then it's off to Silfra Crack. I believe getting good enough with a drysuit to really be safe and confident with it requires not just a few hours of learning but quite a few practice dives with it afterwards.
My drysuit course covered not just buoyancy control but also seemingly simple things like handling a stuck inflator (yeah, the same issue as with a BC), arresting an inadvertent feet-up ascent, selecting appropriate undergarments for the conditions, and drysuit maintenance. All straightforward stuff, but I felt having it taught all packaged together neatly in a course was worth it.