Skyline NEO is boosted, and the boosting chemicals degrade the rubber. If you want the rubber to last for a long time, you should get the non-NEO version.
Personally I am a big fan of the Skyline series. I use Skyline 2 on both sides, though I will probably change to Skyline 3 on backhand after my current rubber wears out.
Skyline 2 lets you hit very slowly if you want to, and it lets you hit very fast if you hit hard. It has a very large range of speeds. Skyline 3 is faster overall, but not as fast as Skyline 2 when hitting as hard as you can. It's worth noting that the Skyline series was made specially for penhold players, but some handshake players like it as well.
My personal recommendation would be Skyline 2 for forehand and Skyline 3 for backhand. If you don't feel so strong with your backhand, it might be a good idea to use Skyline 3-60 (which has a softer sponge). Hurricane 3 is also a good option for backhand.
Answering your questions:
1. I think Skyline 2 and Skyline 3 are both very good. They have slightly different characteristics and I would recommend trying both of them to see which one you like better. You can try each of them on the forehand and backhand, and then make an adjustment when you buy your next set of rubbers.
2. Skyline rubbers last extremely long if you do not boost them. Boosting includes buying the NEO versions (factory-boosted). I have had my unboosted Skyline 2 for about one year now and they still play well.
3. Skyline 2 is the best for defense. With a soft touch, you can return the ball very slowly and accurately. This is useful for blocking smashes far back from the table, and it's also good for playing the ball very close to the net in the short game. Skyline 3 and Hurricane 3 will let you block faster, but you will also need to block more accurately.
Xu Xin and Ma Lin used Skyline 2 during their careers, and you can see that it's good for chop-blocking, loop-kill shots, and playing defensively far from the table. Wang Hao used Skyline 3, and you can see that Skyline 3 is good for quick changes of pace/direction, and taking the ball directly off of the bounce.
4. You will get mixed advice about whether it's a good idea to start playing with hard Chinese-style rubbers (like Skyline and Hurricane). Personally, I really liked using these rubbers as soon as I started playing. Chinese players learn how to play with this rubber, and they are the best in the world. At the very least, it is not unreasonable for a beginner to use Skyline rubbers.