No need to be transferred from abroad, a loan will do but the 400K has to be deposited at least 2 months before the first application and 3 months before the second. You need both a letter from the bank (can be a few days old) and the bank book (updated same day of the application). Kor Ror 2 better be recent. Witness you will need at your home the day of the visit. Get an updated list of requirements from the immigration before starting the process because they do change sometimes.
No, always better to cancel the extension at the immigration. Leaving won't cancel it and you will have an open extension that will prevent you from getting another one in the future. Even if you start brand new. As Tod says, always close the loop.
There's almost never the need to go that early for a 90 day. Nowadays they have a separate desk and they are sorted out fairly fast (if there isn't a drive in which is even faster)
