1. Is the passé simple in fact used in conversational speech, such as in this interview?

While very rare, the passé simple is not forbidden in spoken French.

2. Is "fut" in fact the verb être, conjugated in the passé simple, in both of these cases (ie, bolded at the top of the quote of the full passage)?

Yes.

3. What is grammatically going on with "quelle fut ton expérience [….]"? Is "Quelle" actually a subject pronoun?!

Yes, quelle is an interrogative pronoun here, always followed by the verb être. That’s a very common construction, e.g. :

Quel est le prix de cet article ?

Quelle est la capitale de la France ?

Note that "Ma première introduction au milieu cuir fut dans les années 1990" is odd. A better style would have been

Ma première introduction au milieu cuir eut lieu dans les années 1990