One day overstay they probably won’t charge you the 500baht and below 10days they won’t put you on any “black list”.
At point 2 I would say better transfer the visa at the immigration to be safe. Cause the old passport it’s null and all the visa on it as well. Get new passport and go to the immigration it shouldn’t take too long and no costs
Yes if all the flights numbers including connecting flights don’t match you would probably be rejected at the check in. And it’s not nice feeling. I’ve been there