How to get the most out of your year-long, multi-entry Non-Immigrant Type O visa based on marriage.
This visa is currently available at three Thai consulates in S/E asia without the need for proof of funds. Those are the Thai consulates in Savannakhet Lao, Ho Chi Minh CIty and Seoul South Korea.
The requirements to get this visa for this reason are not extensive. You need; the original marriage certificate, copies of the marriage certificate, your thai wife's i/d & her house book listing along with copies of your passports relevant pages and a few passport sized photos.
The Thai consulate in Penang Malaysia will issue this visa but they require proof of 400K baht in a bank account (no seasoning required) OR the notary letter from your consulate stating you get over 40K baht a month in income.
This visa is a multiple entry visa meaning you can enter/exit the country as many times as you want during the validity of the visa (a year from the date it's issued) and you will be stamped in for 90 days. When that 90 days is running out you go to the border, stamp out of thailand, stamp in&out of another country and stamp right back into thailand to get another 90 day stamp. You do this for the validity of the visa itself.
The way to maximize the time in country with this visa is to make sure your LAST entry on the visa is done just prior to the "enter before" or "valid until" date on the visa itself. This gets you one final 90 day stamp taking you to just about 15 months of stay.
Then you need to apply for the 60 day "visit family" extension at the immigration office for 1900baht. This extension does not require proof of financials to get. That will take you to 17 months on a single year long visa. ..
Good Luck.
TLDR : Answer Summary
To maximize your year-long, multi-entry Non-Immigrant Type O visa based on marriage to a Thai citizen, focus on timing your entries strategically. Obtain the visa from specific consulates in Southeast Asia without needing proof of funds, and remember to make your last entry just before the visa's "enter before" date to secure an additional 90-day stay. Following that, you can apply for a 60-day family visit extension at an immigration office without financial proof, potentially allowing you to stay in Thailand for up to 17 months on a single visa.
