In the section: P2SH-P2WPKH
hashPrevouts:
dSHA256(db6b1b20aa0fd7b23880be2ecbd4a98130974cf4748fb66092ac4d3ceb1a547701000000)
= b0287b4a252ac05af83d2dcef00ba313af78a3e9c329afa216eb3aa2a7b4613a
The last 4 bytes "01000000" are not clear to me where they come from.
It's the second option.
It is the 'Transaction ID' and 'Output Index' of the input(s).
You can refer to the other examples which work similarly but used different sighash flag that are different from the prevIndex.
Yes, that's plausible.
I'd like to send you merit, but I don't have any more.