[susan53]

1/2/3. There's a grey area in the middle of concession and contrast - which is why a lot of accounts lump them together. These are typical examples.

4. Yes. Whether the discourse is spoken or written, the style may change. Spoken language may be formal (eg some speeches), neutral (eg a conversation with a doctor), or informal (eg chat between two friends). Written language may be formal (eg a legal document), neutral (eg these messages), or informal (a quick e-mail message to a close friend.) So while it's true that features such as subordinate clauses are less common in spontaneous spoken English than in written language, it's a matter of frequency, not an absolute.

5. No - it's somewhere on the scale between quite and extremely.