How many wallet.dat files can you manage at the same time?
As many as you want.
What is the difference between using the native segwit format (that begins with b) from the one that begins with 3?
Is it just a temporal way to use segwit until the ones that begin with b are available or there are any pros and cons?
Native segwit addresses (bech32) make native segwit outputs which are smaller than the P2SH nested ones (3.. addresses). This saves you 22 bytes when you go to spend the output.
Sorry for so many question, but I got additional ones:
-I see that bech32 addresses have bc1 at the beginning, is this the part that will always repeat to recognize the segwit transactions?
-I also noticed that there isn't a single character with capital letters. How come there are no caps at all? Im used the classic format and seeing it all in small characters is pretty weird. Im not even sure of legacy format being caps sensitive, but I think it was easier to recognize the shape of the address if there are caps on and off or maybe that is how my brain works.
About caps sensitive.. what would happen if instead of 12sziC91z7hwfpVDNw7UbsisaapBwFtW7t you send BTC to 12szic91z7hwfpvdnw7ubsisaapbwftw7t ?
-In the case of a split into a fork of BTC that doesn't support the segwit format... how would you receive your share?
For example if the BCH fork happened after segwit got activated and you were holding 1 BTC in address bc1qzjw3jywhf2r7k24y3gqj0fs4apddg03pujsjzx, how are you supposed to receive your 1 BCH on the other chain?