How do I answer the expected salary question?
With a range anchored on evidence, and the question turned around first: asking what the band for the role is costs nothing and is answered honestly more often than people expect. If the answer is refused, that is information too.
How long should a take-home exercise be?
Under three hours, with a stated cap and an explicit instruction to stop. Anything longer selects for people with free evenings rather than for skill, which is a filter most teams would reject if it were stated out loud.
What is actually worth asking at the end?
Concrete process questions: how the last incident went, how long the last change took from merge to production, what happened to the previous person in this role. Culture questions get culture answers; process questions get facts.
How long does this usually take in practice?
An afternoon to do it properly the first time, then minutes when it recurs. Most of the first afternoon goes into discovering which of the defaults do not match your situation.