My play time has not been all that great either but I am learning from some of the best. So, again, the grain of salt thing.
Looks like you are working with 3 TIEs and 2 TIE advanced. Unless you have other ships available I'm going to assume that's the case.
Agree with adding Swarm to Vader. You don't have to pick the Storm, you can spread the love around to whoever has the best shot on whoever you want to kill. Cluster missiles are cool, but look at Concussions too if you really want to run missiles. Same cost. If used at range 3 they have one more attack die and do not give the defender a bonus. Yes, Clusters let you attack twice, but max at range 2 and do not give you a bonus at range 1. If early on you can set up Vader to Swarm your other Advanced when you are both at range 3 from an intended target, you'll have 8 attack dice and no defender bonusbefore anyone else can shoot back. Early kills will be helpful.
Storm vs. Tempest, no real reason to go with the higher cost since Vader is likely going to be helping out. No real reason to be worried about being "blown out" early either, since you have the shields to prevent that. With Vader in the mix, another TIE Advanced will not be a priority target.
In the same vein, no real reason to pick Obsidians over Academy. Obsidians would have an advantage over Rebel Rookies, but that's about it. Again, it's likely that Vader will be Swarming these up as necessary. I think the four points could be used better elsewhere.
Which brings us to the final TIE. So far we have:
Vader + Swarm Tactics + XXX Missile - 35
Tempest + XXX Missile - 25
Academy Pilot x2 - 24
Total 84, so 16 points to play with. I like the original idea of Backstabber at 16, because he's totally free to detach from the rest and work into a position where his ability will come into play - i.e. behind an opponent. Dark Curse might not be a bad choice either, especially against a squad running Dutch that relies on target locks for reroll. Night Beast or Winged Gundark too, depending on which ability you think would be advantageous.
However, I would strongly consider dropping one of the missiles and using those extra four points to pay for Howlrunner with Swarm Tactics. Chaining her Swarm ability with Vader's, and having her reroll ability for everyone within range is huge. Of course, the downside is that you have to keep most of your squad in range 1 of her, which requires some planning.
Good luck, I hope this has been helpful rather than confusing!