Definitely don't recommend flying spinnaker only... very difficult to douse if the wind pipes up unexpectedly, and tough even if it doesn't.
I understand your thinking, but it really shouldn't be a problem even then. The key place I've seen people come unstuck is when they don't/can't completely
ease the sheet before starting the drop - the spinnaker clew should be flying out the front like a flag during the drop or else, yes, you'll be in strife.
That's the other point: Something we were taught from a young age in dinghy racing is never
, put a knot in the end of your spinnaker sheets!!
Every other halyard or sheet is fine to stop - but not the spinnaker sheets, because if ever you find the boat getting out of control whilst the spinnaker is hoisted, you need to be able to let the active sheet go - right out of the boat if necessary - and have the sail fly out the front like a flag whilst you get the boat back under control. The safest way for a beginner to lower the spinnaker is to start at the pole/guy end anyway, so you don't really need the sheet to get it down.
..and a general rule of thumb across all classes and sizes is that the ideal length for a spinnaker sheet is 2x the length of the boat on deck.