How many books should I read, or what book is good, to have a adequate defense against a master ?
That's hard to say. But I can say that training, playing games and practicing with puzzles does more then watching video's and reading books. if you like a recommendation then a good book would be Learn from the Legends by Mihail Marin.
Firstly, how important is it to spend a lot of time remembering openings. I'm talking about my level here (around 1850 rapid, around 1700 FIDE rapid) and I'm not interested in playing fast time controls.
When I meet someone about 200 rating points above me in a slower time control, I need to know how to get into a decent position at least in the middle game. And pawn-breaks are my weakness, as well as surviving pawn-storms or avoiding them happening to me in the first place.
As someone of 60 years old who in my youth was playing for my school and my university but pretty much gave up for many years at the age of 22, do I have much chance of making any progress now? (I'm not looking to get a title but 1900 FIDE / 2100 sort of rapid on here rating would be nice, albeit I'd probably never get a game at a slower online time control with increment in that pool and probably face a lot of engine users)