I was told as follows: (answers are in your question sequence)
1 – Optimal is starting with everyone else, but as long as there are still people standing, you’re in the clear.
2 – See above, but from Yishtabach till Shemonah Estrei, you can’t skip anything.
3 – everything except Baruch Sheamar, Ashrei, the last Hallelukah, and then its on to Yishtabach (from then on, its no skipping)
4 – Sort of. You can keep pace, and then say kedusha with the shatz, but then you miss all the omains. Best would be to start as soon as you can and catch as many omains as possible.
5 – If you’re smack in middle, you can’t say any part of kedusha. If you start and keep pace, see above.
As you can tell, I’m a pro at falling behind / starting late. Most mornings, I start at one minyan, fall behind and then pick up a later starting minyan (one of the benefits to davening at a minyan factory).
Not the ideal perhaps, but surely better than putting on talis / tefillin, davening from brachos trhu SA in 9 minutes (which I have seen, but cannot understand how the people do it)