Despardo, Bangkok is one of the safest cities in SE Asia. Much of what you say used to be true, but things have gotten much better over the last few years. Many of the street vendors have been moved to dedicated areas, or are allowed in busy street areas only a couple days a week.
I dont use tuk tuks at all. But again, government has cracked down on them a bit. More customer friendly now. Not to say there aren't a few bad apples. A hot dirty ride. Use taxis, very cheap, or as mentioned Shytrain.
As an American, I've never been taken advantage of. Though I have many times been asked if I want a boy or girl, I just say no and that's the end of conversation. This usually only happens when you are alone.
The Montien Hotel is in a great location, but as I mention in a previous post, same problem as Rose Hotel. They are in the middle of a big construction zone. The OP mentioned only needing a couple of nights and wanting Tawan Club.
That's why I say Tarntawan or Raya. Tarntawan has lost its luster, but very customer friendly and if only 2 nights, location can't be beat.
Your right about the heat and humidity. Spring time takes as much A/C as you can find.
I live in Bangkok 6 months out of the year. My US address is in South Florida. I spend lots of time in the heat.