After following your guide up to 54lvl I wanted to share my own observations. Your guide was very helpful and enlightening for a started, but I have to disagree with a few points.
I wanted to clearly state one thing. Current meta, due to Rogue One units is shifting, however I tried to make unbiased observations following only current gameplay usefullness.
After battling with my thoughts for a few days and weighting in pros/cons I would encourage tweaking your guide a bit. I have to disagree with 3 things.
1. Boba should be above QGJ on priority list. This is an opinion based solely on the main focus of your guide - arena squad. Boba is too valuable, too fast and has too much utility to go with QGJ over him. I agree that he is hard to gear and isn't as useful in raids/gw. However take into consideration that we're talking about a starter accounts. By 54lvl I have almost fully farmed QGJ from cantina. As such, he is long capped out with gear (as other main toons). If I went with Boba first and QGJ second from store, I'm quite sure i would have them both capped out (lvl, gear and tier) around my 66-69lvl. By that time - if Boba was too tedious to gear, you could easily switch him for QGJ.
2. Phasma is a mediocre unit to farm from GW shop. Her usefullness is limited because of 2 units - Boba and Biggs. First breaks her, second makes her his b****. I didn't mean it that you can't farm her. Just saying that she is made irrelevant, by those 2 units. By the time she can actualy make an impact, you're usualy down to 3-4 toons. Having said that, going with Biggs is better for starters. He is a strong attacker and his adrenaline rush is definitely undervalued here. Even Teebo is a nice option here.
3. It's hard for me to believe that your team of Phasma, Lando, STH, GS and QGJ was able to get top5 spot for weeks as you claim. Maybe I'm just a subpar player and don't understand this game well yet. My observations are based only on arena fights and my usual struggles against top10 whales in my bracket. It's safe to assume that being a f2p begginer you'll be underleveled, undergeared and have less good units with lower tier rating than all those whales out there. Oven moreso when mods get unlocked and you're up against 180-200 speed units, while having 130-150 speed yourself. Taking all that into consideration going with an all-out-dps squad like you suggested is pure suicide (been there, done that). To stay in my top10 I had to go with JC just to make it to round 3 against strongest in my bracket. With all that in mind I have to sincerily disagree with your team composition.
With all that said I would suggest to change your guide a bit or at least consider tweaking it. I would go with Boba Fett from Cantina shop, Lando from Cantina squad, STH from Arena shop, Biggs from GW shop. For your fifth unit you can switch depending on circumstances between GS, Ackbar, JC. Best choice is a Lando lead, switching to Ackbar when needed. I would also consider farming 40 shards of Ackbar from Arena shop after you get other 40 from Fleet event. Will benefit your arena team flexibility greatly, especially against empire opponents.
I didn't write this to critique your guide, but to share a bit of light from a different perspective. It's hard for me to agree to some of your observations taking into account my own.
DC: for clarification, my bracket is dominated by wiggs/chaze/Lando/EP/Boba/RG/STH teams, so it can easily be considered quite diversified and representative.
With all that being said, I would like to hear your opinion on this topic.