Getting 1 character to 7* and joining a guild that’s doing both Heroic Rancor and Heroic Tank Raids = one of the best early moves. You need to post a score, even 1 point of damage! But then can slowly unlock Raid Han and General Kenobi both of who are really useful!
The best F2P “early” squad = Phoenix. This is because they can unlock EP, Thrawn and have 2 Jedi to help unlock GMYoda. Additionally they are mostly in non-competing farm areas/stores.
Once they are good enough to unlock 7* Thrawn they become much less useful and really only have a place for their ships and Ezra in a Jedi lineup.
You also need to think about building a Darkside team —> Empire makes the most sense, as it unlocks R2D2 (needed for Commander Luke), plus Phoenix should get you 2 Empire (Palpatine and Thrawn)
The third “team“ to build = scoundrels for the credit and training heists —> i would suggest Bounty Hunters e.g. Boba Fett, Cad Bane and IG88 (all are pilots....) and Dengar once you start getting Guild Currency from a guild running raids. If you start Dengar early you will be in a great position to unlock Legendary Chewie later on.