Hi @chiffon,
I know the feeling: I had never bought a phone before my Fairphone, I always got them second hand from friends and family, and I had been willing to buy a Fairphone for quite some time before I got mine. I was looking at the FP1 just when the FP2 was announced, so I continued to use an old Samsung Galaxy SI (and then a SIII for a year) and waited for a special occasion to buy a Fairphone. I’m really happy with it!
From an environmental point of view, It is always nice to reuse phones others don’t use anymore, but getting a nice phone instead of Christmas gifts you don’t really need is also a good idea!
fyi: I don’t use the phone as much as you (almost no GPS, no playing), but it can last two days without wifi nor bluetooth and on flight mode during the night. I usually don’t wait for the phone to be empty, I charge it every day and a half.
I can’t really answer to the other questions, but I don’t see Fairphone releasing a FP3 in the next 2 years and I don’t see them give up on the FP2 these next 5 years. And the community is great, so I guess that it will soon be possible to port Sailfish easily (already possible as I have read in some threads) and Cyanogen (see here).