Obviously there needs to be a transition, but at some point you go from physics to engineering. I suppose it depends what specialty in physics you go into. Nobody can specialise in everything.
1. The boundaries between disciplines are where they are in part by historical accident, and in part because that's what the people working in them find useful - there is no actual fact of the matter.
2. We don't actually know the underlying microprocesses of anything. Effective theories are all we have, and there's no fundamental difference between an effective theory for the vacuum (if it is a vacuum) and one for, say, the bulk of a semiconductor.
This is true of all categories, so not a helpful comment. I suspect someone has a good enough definition.
(I didn't introduce it - it was already being used).
The benefit of taking such a class or reading such a textbook is that these things have been studied extensively, we have good models for them, and it is useful to know because people are still doing fundamental research on it to this day or working on phenomena that are closely related.
Engineering: practical implementation
That’s how it goes in my brain. It’s physics until we can build it reliably, then it’s engineering.