>>527361527
In order to worst luck-proof yourself and 99% guarantee any single Agent/Wengine, you need around 160 rolls on average (if starting a banner from scratch.)
You have a decent shot to get both Shiiza and her ball with 150, but it's all up to luck in the end.

If your roster is small I would advice against rolling for balls though. If you still want to, I'd go for Yixuan's since it'll most likely improve your score/time overall.