So my son and I are just getting started with IA. We have all of the big boxes. Should I keep the components separate or is it best to just mix them all into big piles of like cards?

It may be easier to learn with less options (start with the core box), but otherwise you can combine all.

However, I would keep the tiles from each boxed expansion separately sorted. All missions need tiles from at most two boxes - from the core and upto one expansion. Having them sorted by expansion would then make it easier to set up the missions.

mixing is fine, just remember thou if your playing campaign mix everything before you start not during.

I'm planning to run a campaign for him and a couple of his friends. I guess I should just mix them in.

I would highly recommend you do the core box campaign first, and keep to side missions that are part of the core, just for the sake of learning it all. If you want to do the Hoth campaign, you'll need tiles from the core box and the Hoth box.

Was planning on just running by he core box campaign. How does it work going from campaign to campaign with the same characters?

You start each campaign from the beginning, whether using the same characters or not.

(Otherwise you overload everyone with XP and credits and it just stops being fun. Needing to decide which class cards to get with your limited XP is much better.)

However, I would keep the tiles from each boxed expansion separately sorted.

I second this. I lumped all mine together but then as I started building maps, realized all the extra was causing too much to needlessly shuffle through, so ended up re-splitting them into their respective sets.

I'm running the campaign for my kids as well, and chose to integrate all the Heroes from the boxes and let them pick the one they liked, but also steered them towards "it'd probably be best to have a couple melee heroes and a couple of shooty and/or toolboxy ones to cover all the bases." Ended up with the two jedi (Diala and Davith - not surprised...) and Jyn and Biv.

Also, I stuck mostly with core-only cards (mission deck, imperial decks) but did mix in all the crate/supply cards and all the I-II-III cards from each set. Not sure how that's going to pan out (we're not really far into the campaign yet).