It falls on a Tuesday but is it a long weekend i.e. no schools on Monday as well? And would most places be open on that day?

No extra day off for my kids so just Tuesday. Holidays do not interfere with commerce in Ca. State and Federal buildings and services will be closed on Tuesday. Everything will be open on Monday.

My kids were scheduled to have Monday 10th off too, but now that they're missing a week of school because of the fires, that may change.

Everything will be opened except public schools, banks, post offices. ATMs will work. I don't think public transport will be reduced.

Vetren's Day is one of those holidays that few businesses observe, so Monday will be fine. Tuesday will see closure of schools (though some may opt for Monday), all federal, state, county, and city governments which includes postal services. Banks vary. I used to work in a bank and they would wait until a few days before Vetren's Day and then call around to see who was open. If the majority were staying open, we would as well. If the majority were closing, we would close.