Please help my squad development, I went down the random line! Need to salvage my squad advice.

Stores.
Shipments

The first 4 slots are all low-level gear, but it's available for cheap and what you don't use now you'll crap for relic materials later in your career. BUY ALL THE CHEAP GEAR, EVERY TIME. If it's not those first 4 lots of gear, though, skip it.

Weekly Shipments

I'm worried about your Credit production. I expected your Arena characters to be 2 to 3 levels behind your character level at this point, but they're much lower than that. So I have to ask, what have you been spending credits on? Also, are you completing GW every day? And, finally, how is your guild? We might have to get you a better guild if that is the problem.
In the meantime, DO NOT buy the weekly character shards. It's much more important right now to boost the character level of your Arena squad first, then your Fleet Arena pilots, and finally any Jedi you use in GW that aren't on your Arena squad.
After we address your credit income and are happy with that, go back to buying the character shards that are available for 1Million credits if you feel like you can. Although it's only 20 shards/week, you'll find later that you got a good head start on a whole bunch of toons you didn't realize you had shards for.

Cantina Battles Store:

1. Hoth Rebel Scout => 7*
2. Fives => 7*
3. Cassian's U-Wing => 5*
4. FOO => 5*
5. Old Daka => 5*
6. Poe Dameron => 5*
7. Storm Trooper => 5*
8. Qui-Gon => 5*
9. Pao => 5*
10. Bistan => 5*
11. Jawa Scavenger => 5*

ALL of those toons after CT 5555 ("Fives") (so starting with Cassian's U-Wing on down) are what I call "just in case" toons (or "ship" for CU-W). You're going to need them, but you don't need any of them soon, and you don't know what order you're going to need them since that will depend on what goals you set down the road. (And also, sometimes, opportunities created by good luck with Bronziums or whatever.) So instead of farming the first 3 all the way to 7* & then realizing you need Pao sooner than the toons you finished, but you have to start from scratch, just take them each to 5* and move on. As soon as you have a real plan for one of the toons that requires it to be 7* and not just unlocked, then you can come back and finish it, but it only takes half the time since you're starting with 145 shards.
But if you don't need ANY of them and you have them all at 5*, go back up to CU-W and take each one to 6* in order. Then go back and take CU-W to 7* ... but then instead of taking all the rest to 7* in turn, just keep buying CU-W shards even though you have the ship maxed. Turn those ship blueprints into Shard Shop Currency so you can buy gear with it. When the time comes that you need one of the characters below CU-W on the list, go finish it, then go back to buying CU-W blueprints.
All of those other characters will occasionally drop shards in events or Galactic War or Bronziums or whatever. Some of them will very slowly (VERY slowly) take themselves to 7* without any effort on your part. If you find that they got that last star without spending on them, you win! If you find you need them before that, well, it's a short farm since they're already at 6* + whatever random shards have dropped since then.
There are a couple more toons in the Cantina Battles store (JKG & Mob Enforcer) but they're not really worth the effort. If you're really, really desperate for something to do or if you're just a perfectionist who likes to have every toon, you can take them up after everything else on this list is at 7*.