Unless you go nutso and drink stupid amounts of water, you' re not in any danger. The danger is that everyone tells you "oh you could get dehydrated, drink as much water as you can" and some people follow this advice literally when pinging. Drink 500mL-1L per hour and you'll be fine. In my own experience you run hot but your thermoregulation still works so you'll naturally seek cooler spaces when you start overheating - this is why clubs/raves have "chillout zones".

I can't speak to long term effects, I only took it a few times at intervals of a few months. In my experience, MDMA is the opposite of addictive - if you've had a good night on it, taking more will do nothing for you for a few weeks.