I retired a couple of years ago and moved to the Philippines as a "trailing spouse) (my wife works here). I spent the first 4-6 completely retired and have since worked part-time, which has helped connect me locally. I've also spent a lot of time traveling in Thailand, but haven't lived there. In any case, I thought I'd share a few thoughts to get you started (at least until our Thai residents get in the loop).
I love visiting Thailand, but have always thought it would be tougher to live there full time (my wife, who lived in Thailand for 3-4 years when she was younger echoes this).
Thailand (as I'm sure you know) has great restaurants, hotels, beaches, temples, sightseeing, etc; a big expatriate community; and friendly people. But even though I have visited for work as well as play, and have good local connections, I've found Thais hard to get to know. Language is a big problem....not that many Thais speak English; but there are also cultural differences. Bangkok, of course, is big and chaotic and not that much of the local cultural scene is accessible to non-Thai speakers (and the "cultural scene" is pretty thin, anyway, compared to Hong Kong or Singapore).
So, if you do move to Thailand, I'd think your primary reference group would be with the expatriate community. That seems to have a couple of sub-groups. First, there are full-time workers, primarily on company/government packages, often with families, who you'll probably have little to do with. Second there are "adventurers," relatively young (20's - 40's) Aussies, Kiwi's, Brits, etc; working often at relatively marginal jobs (English teacher); who are spending a few years seeing this part of the world, but sometimes end up staying longer. Third are the "sexpats," primarily there to hook up with Thais, find (or purchase) a girlfriend or boyfriend, get married, etc. And, last, there are retirees who are able to afford a more upscale life in Thailand because of a lower (but rapidly rising) cost of living.
I presuming that you want to spend part of your retirement in Thailand from choice, rather than financial necessity. And, I do think it would be a great place to spend 3 - 6 months a year, so long as you're able to leave whenever it gets to be too much...
And, if it turns out you really like it, you can always stay longer.
I've split my time the first year and spend 2-3 months at the beach (but probably not Pattaya), 2-3 months in Bangkok, and maybe a month or two in Chiang Mai (Chiang Mai is wonderful, but I'd find it a little boring to live there -- you might feel differently). In terms of practicalities, it looks pretty easy to find long-term housing and to settle down in any tourist area. And, even if you come in as a tourist visa, you'll probably only have to make one visa run (and, with cheap airfares, a trip to Hong Kong in the cool season might be a welcome break!)
It's a little more expensive that way, but by the time you were done, I think you'd be in a better position to decide how much time you want to spend it Thailand.
Hope that helps!