1) Timeframe depends on the length. I can pound out an SA entry in a few weeks. Anthology pieces are usually longer, can take a few months. Long projects take years. My current WIP is 5 years old and right at 200K words. But I'm also a slow writer and have a full time job in healthcare (if you know, you know).
2) Hahahahahahahaha yes. This is a constant struggle. The more time available, the more things I find to distract myself. The best option, for me, is to eliminate my main sources of distraction...my phone and the internet. I've had the best results from writing outside or in my car, longhand, during my lunch breaks at work with the phone inside the building. Leaving the house also works well. I can't write in silence without my attention wandering, so I usually listen to music that is tolerable, but that I don't love enough to make me stop writing to listen. Disney instrumentals work well for this, they're pleasant and melodic with no lyrics.
3) I draft everything into one huge document (that I back up in multiple places, I've learned well from past mistakes). I abhor planning things out beforehand so when I need to double check things for continuity, I just scroll back up instead of having to remember what chapter had what and go looking for it. I cut the draft into chapters and proof them again before I send them out to editors or beta readers. This method is good for me but is probably too chaotic for some writers.