a) I used to do it at 42 or 43 in an older oven, and the new oven only does 5° increments, so I tried 45, and it's consistently better.
b) It's done in 4 hours, but the punters prefer it sourer, so usually 6.
c) Not my problem.
d) Not sure I'd fit 5 jars in an air fryer. If I had an air fryer.