Looking for advice on who to invest in/spend mats on.

I just reached SP6. I've been logging in daily to do dailies,etc but have not been progressing story since I got busy with other gachas.

main team atm is Celia, SDalvi, Bride Eclipse, Justia and Nebris. The first 3 usually clears the grid by themselves.

from the sticky, I'm saving mats for Diana and try to +5 her and get Idol Helena w/ selector tickets.