I understand I can extend my single entry non-o (based on marriage) for sixty more days in Chiang Mai, where we are staying. Some questions:

Will a copy of my wife's house registration book do, or does it have to be the original?

Is it a problem if it's from an Issan province? If so, what can be done?

Thanks in advance.

The wife being registerd in Isaan could be a problem, depending on the immigraiton office. Some will want you to extend at the immigration office for the area where the wife is registered, as there you are supposed to be staying with her. Only one way to find out.

You will also need copy of marriage certificate and your wife to accompany you, with her ID-card.