All about GOSI

Hi there, first of all I want to declare that I tried my best to search related terms on this forum about GOSI and couldn't find the details I wanted. So I am creating this new post. If this is the duplicate one for previously discussed things, please post the link here, I appreciate it a lot. And if this is the original one, we have much scope of discussion.
All I understand about GOSI is, it is deduction in monthly pay for social security, against being aged, disability, unemployment etc. For natives, 19% of monthly salary is to be paid, 12% from employer and 7% from employee while for expats like us it is 4%, 3% by employer and 1% from employee. The difference here between locals and expats is because locals get more advantage of this scheme, like pension and unemployment funds etc. The questions banging my brain, which I could not satisfactorily find are

1) What expats get by paying GOSI? What is included and what is not?

2)Is it mandatory? Can I opt for not receiving any advantages provided by GOSI and not paying for same?

3) My employer is deducting different amount everytime for GOSI, how GOSI payments can be calculated?

4)How I get receipt or confirmation of my GOSI being paid on time?

5)I read somewhere about Indemnity, which is on regular deduction of  GOSI at the end of contract period while leaving Bahrain, employee needs to be paid by his/her employer, what is the practical reality of that? Does it exist? What is the exact amount and if suppose your employer don't pay you that, what are options? And if you break contract or change employer what happens to Indemnity?

Sorry for long post. Though this issue is not a big deal, I like to get to know these kind of stuff. Any information is appreciated.
Thank you very much.