you're talking 100k baht not USD right? No issues with bangkok bank, I transfer 70% of my salary each month in only 1-2 transactions. max it takes is 2 business days but usually same day on weekdays
No matter what visa you have, you are gonna have to pay duty on musical instruments. We brought over a container of household goods with my non-b and the guitars were the only thing we had to pay duty for.
It took me 3 days and an online application to get an IDP in Australia, hopefully its similarly easy in Spain, it should also be cheap so just do it either way to be safe