I'll be in Bangkok on holiday on Wednesday 12 October, which I understand is a holiday celebrating the end of Buddhist Lent. 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?

Only the bars close (and not all bars .... hotels bars stay open and some pubs switch to paper cups which somehow makes it OK to stay open).

Shops never close in Bangkok!

This day is NOT a statutory holiday. I think everything should be open.

This day is NOT a statutory holiday. I think everything should be open.

Yes, this is true. The start of the Buddhist Lent (Khao Pansa) in July is more important to some Thais..... even then it's still not a statutory holiday. The full moon in October marks the end of the Buddhist Lent (Ork Pansa) and it's business as usual..... everywhere.