As someone that followed the tips from everybody here and followed their progress, I'm here to tell how I beat the Zeta Challenge, for anyone that might want to know (and see that it's really easy to get the 8 5* ships if you focus on them):
If I wanted, I could have 8 5* ships at level 78 (maybe at 77, but the challenge wouldn't be unlocked), but Maul's and SF's shards were more important. Just got to 79 and finished my 8th ship, but I couldn't 3* star the challenge (well, I got close on my 2nd attempt, maybe the next time I will, but it'll depend on the RNG) and got my first 0/2 zetas lol
For anyone wondering, the Slave 1 farm wasn't slow at all, I'm at 20/85 now, and even Scimitar was a "close 5*" (I'm 25/65)
I beat it with: (All my ships were 5* and level 75. All my toons were 7*, except for JC and TFP, they were 5*)
Boba G10 Lvl 79
Wedge G10 Lvl 79
Biggs G9 Lvl 79
SF G9 Lvl 79
TFP G7 Lvl 75
Maul G8 Lvl 70
Ahsoka G8 Lvl 70
JC G8 Lvl 70
GS G8 Lvl 70
Of course the fact that I'm getting top1 daily in the fleet arena helped my progress, but as I said above, I could have done it much sooner.
Now my question is: I'll keep farming ships from GW (don't really see a use for any other GW toon. Teebo and Phasma would be for Rancor, but I'm not close to any Rancor team, and only the top5 places matter in Rancor, the rest are almost all the same) and keep buying Slave1+Scimitar from the ship shop, but should I use the rest of my currency purely on zetas or should I use it to buy gear? Keep in mind that I'll unlock zetas in the fleet store in 13 days, which would allow me to buy 10 zetas (if I only spend 3k ship currency in these 13 days, because I'll earn 23,4k).
I'm getting to level 80 in 5~6 days (and farming syringes), which means that when I do that I'll be able to G10 Biggs+STH (Wedge and Boba already are). After that I don't know if I gear EP+Maul+Sid for a Zaul, EP+Vader+TFP for a Zader or EP+Rex for a anti Sith, I'll figure out that later.
Well, what do you guys think? Thanks again!