The vetting questions are just personal details, address history, criminal convictions/bankruptcy etc. I believe they should also ask for references however mine didn’t, but I don’t know why!
I believe you may only have 5 days to accept the provisional offer, and if it’s not accepted in that time they may withdraw the offer.
I’ve read different things about the timeline for vetting, seems it can be anywhere from 3 weeks to 8+ weeks. No start date has been mentioned yet as it is only a provisional offer, from what I can gather, they will be in contact at some point after the vetting is complete to discuss a start date.