First thing is to find out how "hard" or competitive your friends want to play list wise, the worst thing you can do is find yourself at odds with how the group wants to play and Eldar have a couple of power builds that are true tourney winning lists.
1. Yeah, the chassis are all pretty close, I personally just magnetized the turrets and picked up some Forge World ones to form the base for if I ever want to run them as serpents.
2. Once again it depends on how hard the lists are gonna be, Storms are under performing compared to Defenders who aren't superstars in their own right but if you aren't playing high end competitive lists you should get plenty of mileage out of them.
3. I'd go one big one, small squads are too easy to lose a guy or two and have them break, plus there's lots of other cool things that live in Fast Attack.
4. Wraithblades look so cool, the new Wraith kit is really nice, I got a unit with Swords and they can really blunt an attack with high toughness as long as it's not a serious dedicated elite melee killer and if you take a Spiritseer to make them troops and lead them you even have the chance to allow them to take on 2+ saves with the right seer power.
5. Quanar has you covered there.
6. There's a couple of good eggs and threads on here if you can get past the hatred. Eldar have gotten a bad rep for not needing tactics due to the tourney scene but if you just ignore those posts you should be able to sieve a couple of diamonds from the rough