Looks to me that your short connection is at KIX, most likely you'll be fine, Japan immigration and customs are quite efficient. You can enter security on domestic flights in Japan up to 15 minutes before departure, and flights don't even start boarding until 15 minutes before departure, also the domestic flight area of KIX isn't very large. If you do miss it, it's a non-issue, there are 7 more flights per day after the one you're scheduled on, they'll (NH) just move you to the next one with space. Since it looks like you're staying a night in Tokyo then worst case scenario you arrive in Tokyo a few hours later than planned. If you are severely delayed in BKK before boarding, then have TG move you to a direct Tokyo flight, they have several flights per day to both HND and NRT, though many of them do not have F class, so you might have to suck it up in C in that scenario.
At HND, you won't be able to access any airside lounges after arrival on the inbound if you have an overnight. There is a very small arrivals lounge that you are entitled to use as an NH F or C customer, but if you're going to a hotel in the vicinity then there isn't really much point. As for accessing airside, you will only be allowed to enter on the day of your departure and the domestic lounge is nothing special at all, I wouldn't go out of my way to get to the airport early.
For SIN, if you don't want to go to the SQ SKL, then there are loads of activities at Changi. Have a look at the airport website to see what's on offer in your terminal. They have designed that airport to be as comfortable and entertaining as possible for long connections.