In reply to owena:
big variations in conditions leading to very different difficulty on the same route on different days
short daylight, potentially very severe weather
very real risk of avalanche
on grade I and II, the climbing is likely not to be the most serious part of the day, and your experience on the hill in winter conditions is more relevant than any technical skills
but these grades are broad, and while i would have happily done NC gully on SCnL the day i did it without a rope (II), i cant imagine being happy to make the crux moves on dorsal arete without one (also II)
though obviously many would find it trivial. so there is no grade that means ropes are required, but your plan to just get on the hill and build up lots of experience on lower grade stuff and then increase the grades organically sounds a good one
lots of brilliant low grade mountaineering ground in those ranges, up bristly ridge, down y gribin was a fantastic day out, we used a rope, many wouldn't,
cheers
gregor