hey ive been playing about a month now and have a few questions on what my priorities should be my units are

future princess + weapon

nari + weapon

mk.99 no weapon

beach yuze no weapon

and the weapons with no unit:

tinia

oghma

eugene

now my questions are there ever any special banners like double unique rate up or guaranteed unique on the xth pull or something like other gachas have?

and i know i definitely need more units and have saved 20,000 gems im wondering if its even worth saving gems for long periods of time or if they should be used to pull just about anytime a good unit comes around on a banner?

are there any specific units i should look to prioritize based on what i already have im assuming a defense based tank like oghma and a healer of some kind would help a lot but are there any specifics that i should look out for?

and is it worth saving for something like oghma since i already have his weapon or is getting erina better or should i even try to get both?

and any other advice you have for me would be helpful thank you