Redundancy, Curtailmentt and BRP

I am working with an employer and thinking to change jobs but do not want to notify current employer before i get a visa from new employer. I have few questions

a- When i will send my Old BRP will it be retained by home office if new is issued?

b- Can i notify my current employer after i recieve new BRP if i do have two months in new job and current notice for current employer is 4 weeks

c- If by any chance my new visa app is not approved, will i be returned my old biometric card and will my current leave remain as it is?

d- If i leave my current job and they notify home office and they send me a curtailment letter then if i find a new job and apply and application is unsuccessful then do i still have right to make new applications if my curtailment date has not exceeded(i.e can i make multiple tries) as long as my curtailment date has not been passed if one try fails?

e- Someone said if application is refused you have to make new one from your own country. I believe that is only the case if your current leave expires and curtailment date has been elapsed as well. If you are within country and your curtailment date has not passed, you can make multiple applications i.e if one is unsuccessful, you can make another?

f- Someone said there is a 28 day risk window after curtailment date. If you find a job and visa in that day home office ignores this time but if you dont find a job and exceed 28 days after your curtailment then it is considered over stay? Can someone comment on it because i have someone who is waiting for lisence and wants to sponsor me and that can take long time

g-If i leave current job and find a new job before crutailment letter comes then based on my knowledge it will superseed last job and then i shouldnt have to wait for curtailment letter and i might not recieve any curtailment letter at all.

Thanks,

Bholo