You travel enough as most of us have and you understand that the majority of IO's are the same, I wouldn't worry, it's their opportunity to flex. I've just come back to England and the attitude of the coach driver is enough to U-turn. 😆 your back, just smile. Always ask for a supervisor as alot do not understand this visa or these new modern ways, most have never left or probably understand our attraction, to them it's just another day in paradise 😀
Think it through, how will you play the instrument when it's in another country! Or paint or whatever, If you play it in Thailand then you need a work permit.
It's valid and covers the travel dates, yes recommendations are 6 months validity, you will probably have border control make you aware, that's what happened to me. Remember they don't carry over time anymore, so applying early means you lose 6 months.