> I'm also curious whether you get a tolerance, so that heavy drinkers need to drink more to recover the same amount of energy. Can anyone give their experience?

You don't have to go by anecdotes: caffeine is the most popular drug in the world and has been studied fairly heavily. It improves focus and some other cognitive metrics for a short period of regular use, and then your daily hit of caffeine just brings you up to what your baseline used to be.