Depends how mainstream or obscure your collection was. You'll get plenty of choice at a record fair, although prices could be a bit higher than you'd pay on eBay or even Discogs. And will also depend on whether you're after absolute top notch condition, or are happy to settle for Very...
Depends on what it is, and what condition the vinyl, sleeves and inners are in.
Best check on eBay. A local dealer may be the other option but she's unlikely to get much for them that way.
Absolutely. Mostly buy second hand vinyl these days, digging up long lost gens or finding new ones. Buy and sell on eBay and regularly rummage in charity shops/jumble sales etc
Still use a Sony hifi I've had for years.