Just to add to what sora and lolix said, remember that this is a Star Rush event, which means you hace more time to prepare for it. Don't be in a rush and try to complete them too soon or that decision will mean a waste of cha/sta. The videos in the guide provided by Lafate are usually a great entry point for new players. Study each map and plan accordingly. You should be fine. If you want Beatrice try to complete up to the fifth map at least. If you only care about Marie, the first four ones sholuldn't be that hard if you take your time to get ready for them. Fifth one can be a pain, though.

Regarding gachas, that's the nature of the game. I know the pain... I'm sure that luck will come sooner or later. I was in your position until I suddenly got 2 black pulls back-to-back. Don't lose hope!