Woah wait 5m-1hr in SP to enter the lucid dream? No way, < 1 minute definitely. The whole process can take up to an hour to pull off, but once you have SP you're ready to roll into the dream (or roll out if you are doing an OBE). Just imagine rolling into the dream scene before your eyes and you'll enter fully lucid (feels like a rollarcoaster ride!)

As for external things waking you up; it'll be the same as if you were asleep. It would take a significant sound to wake you up.

Breathing is a hallucination to SP; it makes it feel like you aren't breathing, but you are. Same with the racing heart I believe.

WILD is far easier if you're proficient at it, otherwise DILD is the way to go. Personally, I just DILD and chain DEILD when I wake up, seems to be the most effective.