Night training questions

We are starting to think about night training our 2.5 year old. He wears underwear during the day and a pull-up for sleep. He still wakes up pretty full. There hasn’t been a time he has woken up dry— ever. The little research I’ve done so far points out that there’s a specific hormone that the body produces to stop the ability from peeing while asleep and it’s not a good idea to start night training until they are waking up dry. Is this really true?

We are also struggling with how to limit liquids before bedtime. I know this may sound like a silly question, but I worry about him getting thirsty. He has free access to his water throughout the day and he also gets it during meals/snacks. But he also requests it right before bed. We keep a water bottle in his bed too in case he wakes up thirsty. Part of me feels like he’s just drinking it out of boredom, but another small part of me is worried that I’ll be cruel for taking it away from him and he’s actually really thirsty. How do we know if they’re actually thirsty before bed?