How often do I need to renew my retirement visa in Thailand and can I vacation there without a visa?

You as a US passport holder get stamped into thailand without a visa for 30 days on what's called a visa exempt entry just like you have on all your trips here without a visa..

You have several options.

Get a year-long, multi-entry Non-O visa based on marriage to a thai (there are places that will sell this visa without any proof of funds). That visa would let you get stamped in for 90 days at a time and you can get 15 months of stay out of it (in 90 day increments).

You could get a 90 day Non-O visa and then extend it either based on marriage or on being over 50 by meeting the financial requirements.

Just so you know IF you're wanting to use monthly income to meet the financial requirements the US consulate here no longer issues affidavits of income from abroad notary letters meaning you would need to transfer from overseas into a thai bank account in your name only the required minimum amount each month EVERY month for the previous 12 months to get the extension. If you can't/don't want to do that the only other option is using the banked money option where you bank the required funds in a thai bank account in your name only to meet the proof of funds.

OR

You could get a year-long, multi-entry Non-Immigrant Type O-A visa from the thai consulate in the US (Chicago, Los Angeles, New York or Washington DC only). That visa requires a police back ground check, a medical certificate AND starting on Oct31st proof of insurance BUT you show proof of funds by using your account in your country.

Here's the information from the thai consulate in LA about the O-A long stay visa.