Well any good tuner will do a boost leak test and ensure all system sensors are good to go before tuning. If something is flaky during a tune it will definitely present itself and make tuning a nightmare.

Boost leak with a MAP based tune isn't going to really matter. The only thing you'd have to worry about is compressor efficiency and extra heat. A boost leak won't really effect the tune.

Water temp sensor should be simple to see if it's bad or going bad. You can see the sensor voltage or reading while driving around otherwise log it and go drive around. I've had a coolant temp sensor spike down to like 30 degrees a bunch of times, but never would have known if I wouldn't have seen it in the log.

Where are you and when are you available?