Well just a few early tips and things to mention before I head out.

Don't draw the single 300 jewel/nutaku gold gachas. I don't believe it's ever stated in-game but drawing 10 gives a guaranteed SR or above, which is mentioned in the How To Play section below the game and when paying for the transaction if doing gold.

All weapon effects take effect but it doesn't work the same with Eidolons. So only use weapons corresponding to your team's element unless you want to waste potential skill bonuses but you're free to use whatever sub-Eidolons, only the skill of the main (and friend support) one matters.

Several standard tier souls can be unlocked for free but watch on who you decide to unlock afterwards as they cost soul p to unlock which is only gained from leveling. Legionaries cost 500. You get 30 each level, so that's 17 levels. I'm at Lv35 and it's already taking me nearly a day to level once (without using AP recovery items)