[2019] How fast does your hunger meter decrease

From my personal experience, I've never had food be an issue. There's plenty around whilst you're playing the game, in pretty much every biome too. It'll decrease quicker when you're super active and possibly based on weather too. I feel like once you're playing on a populated server, you will be using it quicker - but at the same time, you'll be able to steal from farms, kill them for meat etc.

It really depends. Your stats naturally drain very slowly. However, certain things will increase this rate.

Hot weather makes you drain water more quickly due to sweat, while cold weather makes your body burn food to stay warm.
Running costs stamina. Draining stamina costs water, replenishing it costs food.
If you're injured, your body will consume food more quickly to repair itself.

So if you're hurt and running everywhere and it's cold, you'll go through food quickly. If you lay down in a nice temperature, it can take a long time.