my first 2 marriage extensions were multi entry because we traveled was either leave for a trip or do a 90 day report my choice just had to do the 90 day report 90 days after I entered the country.
Last 2 just extensions because of Covid we didn't or couldn't travel so I save the reentry permit costs
They will possibly do a house visit as well I've had them out to the house for my first marriage extension and a phone conference for my second depends how busy they are and how far from immagration you are
You don't need to apply for a new visa you get a visa extention for a year based on marriage on your current O visa.
You can live at any address you just need to register where your living so you'll need mums book or a copy of it and I'd imagine a letter from your wife and mother saying your living there. Take photos of you at the house inside the house with your wife show the house number in at least one photo.
Sorry we rent at the moment so just needed the landlord's book for the process.
You'll probably get a form put in your passport stating your address.
O visa lasts for 3 months then you apply for a years extention if you don't apply for the extention every year you have to reapply from beginning again