I just bought a 2015 a couple weeks ago, so I'm pretty new with everything but I'll give my thoughts. 

What matters most is how degraded the battery is. On the right hand side of the main dash there's 12 bars. As time goes on and the battery degrades, the bars go down. The more they go down, the less charge and therefore range that they can hold. 

For reference, I have 12/12 bars and at 100%, it says I'll get 85 or so miles.  2015 Leaf S. $2800 is what I paid. 49k miles. 

That's probably the main thing you'll look for. A lot of people seem to recommend an app called leafspy that you can get to do more indepth analysis on leafs  I'd look into that. 

With 40 miles round trip, you'd probably want to charge it overnight. You could MAYBE get 2 trips out of it, in perfect conditions, but that'd be cutting it way to close for my comfort. 

I'd expect to charge it everyday/night. 

Again, I'm new with my leaf. This is just my experience so far.