https://swgohindepth.com/ultimate-zeta-farming-guide/
If you see the video above, this guy used a lvl26 Executrix with 6* G6 lvl69 Tarkin. All ships lvl 78 though. Okay then, obviously one can do the Zeta mat challenge with a low lvl Tarkin. But then I would skip QGJ until after the zeta mat challenge and farm ship building mats in the arena store instead. At least when you are "only" top 10 in the fleet arena, you won't be able to upgrade your ships to lvl 78 with the mats you get there.
For me that's too late and also I don't have my 8x 5* ships ready. It would also mean to farm another ship (CS/TFP) earlier and skip on Maul/Sun Fac instead.
Actually I don't think the guy from the video was f2p. Probably he bought some fleet data packs, where he got his mats/ship plans from. You can also see that at 0:47 he is rank#1 and has 135k fllet power, whereas his #2 has 120k. So that's rather p2p. And: he is lvl81. With lvl81, we will also be ready for it. My Tarkin is 6* now with lvl 79.