In my opinion, you wont go wrong prioritizing CLS.
For CLS you need certain rebels, and r2.
For r2, you need empire.
Of the rebels, biggs and wedge are amazing in arena until CLS. Leia will outdamage most when she has r2.
You also need scoundrels, probably before anything. Some of them are also rebels. Boba Fet is not a rebel but good in arena too.
The next character you need is Thrawn, who is second in importance to CLS in my view, so you need phoenix.
Finally, resistance will dominate Galactic War, Territory Battles, and give you speed mods. I am prioritizing resistance over phoenix, because speed is extremely important in arena.
You may want to get your phoenix to g8 or g9 and start upgrafing other characters for arena as you hit a brick wall in climbing (which you will with phoenix)
When you join a good guild, meaning one that does heroic raids, you can earn GK and Han Solo shards. You can only earn these shards in heroic raids.
This was basically my f2p strategy. You could go for phoenix first, but i wanted to prioritize my arena team for crystals. Now when i get shards for phoenix, i have not missed months of gearing for arena. I missed thrawn for the last event, and this one a month later, but i am ready for CLS. No regrets, and no impact on my arena top payout performance.
