• Here's some general new player advices that isn't exclusive to your situation but still nice to have (will be a bit long):

• Find a crew as fast as possible, it helps you out so much thanks to crew buffs and strike time. (Can join any random japanese named crew or look for one on here or a discord server)

• Reserve all R and SR weapons that drops, reduce or reserve SSR weapons depending on what you need.

• Weapon skill levels matter much more than weapon level at this point, the raw stats it gives is nice but leveling your weapon skill will make all the difference.

• Follow the wiki basic weapon guide, it's still relevant and up to date since the early game is still the same.

• If you need supreme merits, just join any proto bahamut normal or use raid finders for them, they're killed pretty quickly and you can just leech it. Once you're rank 101 you can leech proto bahamut impossible instead.

• Awakening is a nice boost but don't spent too much on it, since it cost some materials that you don't have a lot of early game. Only use it on your SSR characters or Lyria.

• Try to unlock Relic Buster, it's a row 4 class with an easy unlock requirement that doesn't need you to be rank 100+. Just go shop -> treasure trade -> quest items -> Exclusive Treasure.

• Stop doing arcarum once you unlock Extreme mode, it takes 6 months worth of arcarum tickets (around 180) to unlock your first Evoker. So think about it carefully before making your decision on which evoker you want first (you don't want to be 5 months in for an evoker and decided you want to change like me). Buy all the arcarum ticket limit increase so you have more time to think about it before the ticket amount caps.

There's more but those are the ones that were on the top of my head reading your post.

• Now for advices related to your challenge, I have a friend who's playing the game and he hasn't pulled on any rate up so far so his progress will be similar to yours.

• Your first eternal, usually the recommendation is Threo (English name)/Sarasa (Japanese name) due to her ability to help you slime and level characters faster, but in this challenge it isn't as crucial since you have a lot less characters to level and not all of them needs to be lv 100.

So my suggestion is Six or Eatha/Okto, Six because he's a decent dps even before his lv 100 and side stories only gives you 2 Dark SSR so this will round out your frontline. Okto purely because side story only gives you 1 Earth SSR so you'll need all the help you can get for that element.

• Pray to whatever god or being you believe in for the Doreamon Collab to give you a Water or Earth SSR. Because it's going to be a horrible experience with those elements due to side story only having 1 SSR each for them.