1. It's the same basic map as the mod. It's the same main island/continent, and all the large cities are in the same locations, with largely the same loot spots. They've added new places, like a few military bases and some small towns, added a few things (most notably a shitton of military loot to balota airfield on the coast), and removed very, very few things.
2. You can drink a water bottle to 0% but atm there's no way to refill them, at least through every way I've tried. They're the best method of hydrating, but once they're done, they're done. Drop any 0% food or drink you find.
3. The background color changes from green to yellow to dark yellow to red. Once it gets to red, you're in deep shit and need to drink/eat asap to avoid dying. Your character will start telling you through the bottom left text "I'm starving to death" or "I'm dying of dehydration." Once you start seeing "I really need to drink" or "I really need to eat" you should do your best to find food/water as soon as you can. Sodas/sardines will give you a bit of both, water spickets will give you unlimited drink, and rotten food is a near guaranteed death unless you have charcoal tablets.
Added you on steam.
