I'll be holidaying in Chiang Mai on Sunday 23 October which I understand is a Thai holiday commemorating King Rama V, with a public holiday on Monday 24 October. I heard that "everything" shuts down on Thai holidays, but does this refer to just places that sell alcohol, or all shops and businesses? How is the tourist area affected; tours and suchlike?

You'll upset the "I've gone Native" Brigade with this sort of post.

Don't worry too much. You'll find a beer somewhere. This isn't a "close everything" holiday.

I can't think of any Thai holiday that closes tourist oriented businesses. On Rama V Day and the following Monday most shops and private businesses will keep their usual hours. Schools and government offices will probably be closed on Monday. I'm not sure about banks. I don't remember if this is a bar closing holiday, but even if it is there are always a few places that keep serving. Bottom line is that most businesses that tourists are interested will be open.