There is only one, albeit huge, terminal in Suvarnabhumi. All domestic flights are located on one side of the terminal, you cannot avoid walking from the international end to the domestic end. It is more convenient to book the 2 flights together with the same airline all the way to Chiang Mai (even though your airline may use a code share arrangement for the Chiang Mai flight). Otherwise you have to retrieve your luggage in Bangkok and re-check in. When you have a single booking everything is taken care of by your airline, much less hassle.
You need to leave after every 90 days stay if you have a non O multi-entry visa applied outside of Thailand. You only need to report your address every 90 days if you have a visa extension obtained in Thailand.
Chiang Mai immigration office stopped requiring filing a new TM30 on arrival, if your address has remained unchanged. I arrived 2 weeks ago and asked the question.
This applies to the non O multi-entry visa purchased overseas (that does not require a separate re-entry permit) but does not apply to the locally applied year extension (that requires address declaration every 90 days, and re-entry permit if you leave the country and want to re-enter on the same permit to stay).
The yearly extension does not allow you to travel out of Thailand and in again. If you want to leave Thailand during the validity of the extension you have to buy a separate re-entry permit (single for THB 1,000 or multiple for THB 3,800) at any immigration office or immigration counter at an international airport before you leave the country. This re-entry permit will have the same length of validity as your visa extension. If you do not buy a re-entry permit and leave the country your visa will be lost.
Ideally you need pictures of you and your wife in front of your house, showing the house number, and you and your wife in your bedroom. Once you have submitted your application they may send someone to your house to check whether you live there.