The only card you really need from Kayn is Rule By Fear, his deployment card is terrible in Skirmish because it's overcosted

http://cards.boardwars.eu/index.php?album=Ally-and-Villain-Packs/Wave-2/Kayn%20Somos/

Don't think Hit & Run is a must-have command card from Echo Base Troopers, I've only used it once or twice ever, skip unless you really want to run the elites in a list:

http://cards.boardwars.eu/index.php?album=Ally-and-Villain-Packs/Wave-5/Echo%20Base%20Troopers

You don't really need any of the cards from the Stormtrooper Villain Pack, since you get the best cards, Reinforcements, from the Rebel Trooper pack. And you get plenty of Stormtroopers in Core.

http://cards.boardwars.eu/index.php?album=Ally-and-Villain-Packs/Wave-3/Stormtrooper

Consider Blaise for Intel Leak if you want to run spies:

http://cards.boardwars.eu/index.php?album=Ally-and-Villain-Packs/Wave-6/Agent%20Blaise/Command%20Cards

New Jabba's Realm stuff seems universally good with possible exception of Alliance Rangers. Scum will want Jabba for sure.

-1x Stormtroopers
+1x Blaise

-1 Echo Base

+4x promo cards, 2x eRebel Troopers, 2x eStormtroopers

Stuff ordered, thanks all!

-1x Stormtroopers

+1x Blaise

-1 Echo Base

+4x promo cards, 2x eRebel Troopers, 2x eStormtroopers

Stuff ordered, thanks all!

You don't really even need all that to have a good experience. I played with just random figures before I ever got a core set. My friend had the core set and a team I had Boba Fett, Hired Guns, Bantha Rider and IG88 and I had a blast. My command cards were whatever I had and could fit in a list and he let me borrow a couple from the core set. I think you'll have enough to set up 3-4 people playing. Most of the questions you had in the original post could be answered by this

"just play the game"

sometimes you just need some games under your belt. There's no hard or fast rules as to how you have to play. I usually do themes and find that I enjoy my list a lot more. Some of them are more competitive than others but sometimes you just need to play what works in your hands. Not everyone plays the same, and some of the figures may respond better to your playstyle than what you read on a post here in the forums. That can be found only through some play time.

"just play the game"

The best way to get started with IA is to play a game with the tutorial scenario as it's kind of a mix between campaign and skirmish. From there just play skirmish or campaign (depending on your group's interest) with just the core or whatever you have on hand. It's only once you've completed a few missions/matches that you need worry about what figures are the best etc.

99% Agreeing with the two above.

If you want to play scum as your primary faction, as I did, I would rush out and buy either Greedo or Hired Guns asap. Scum doesn't have a lot of different stuff in the Core. That'll give you a scum army anywhere between 26-36 points. Then you can ally with rebels for the rest. Both of those are excellent objective grabbers. Ally with some rebel support dudes and you've got yourself a fine starting scum squad.

Nah dudes, just go hard and dive deep. I'm already familiar enough with FFG game systems that I know that whatever I get in will be a good experience for me. I've already started building a playgroup and reached out to local TOs to see what kind of events they have going on. It's going to be fun, thanks for the help.