with the one year one I had to do a border run every three months, just in + out, but that was it. I did post myself asking about this and I'm in the process of applying for one in China, I'm submitting my application today. It doesn't say how long they will issue it for but I believe a MULTIPLE ENTRY is a year, why would you need a 2 or 3 month multiple entry?
as I said in my post I have been out of the country for a few years working in China and planning to return this summer. When I was last in Thailand, I used to be able to go to Laos or Malaysia once a year and get a one-year multiple-entry O Visa and all I had to do was show my marriage certificate and wife's ID card.
even to stay here on a retirement visa you need to maintain a minimum balance of 400k and a balance of 800k for a minimum of 3 months prior to your application. To establish a business you need a Thai partner who will maintain a controlling interest in the business, ie minimum 51%. These are the regulations. however, you can get a one-year multiple entry visa (based on your marriage to a Thai?) prior to coming, which will only require your leaving and re-entering every three months (a day trip to Cambodia and back would suffice) if nothing has changed recently. This is my current plan and worked for me for 10+ years.