I've not been to any of these places, but I'm not going to let that prevent me from giving advice. My wife says that is a fault of mine, but I don't see it that way

I think that MikeFromTokyo is correct. It is might be too much moving around. Don't forget, for the most part, any time you move from one place to the next, it's a lost day. Maybe do Bangkok and one of the other two cities (plus Maldives)? Would you skip Maldives and concentrate on Thailand? If you stayed longer in Bangkok, could you do some day trips?

We're actually going to Bangkok in December and we're staying at the Shangri-La. It is on the river (I suppose that's good) and very near the Mandarin. I believe the Mandarin is nicer, but we couldn't justify the difference in price.