I'd suggest checking manga forums or dedicated Bleach fan sites. They often have detailed breakdowns and recommendations on where to pick up after a specific part. Sometimes, the author or official sources might provide cues as well.
Well, it's quite a challenge but possible. First, decide on the main idea and the ending. Then, sketch out the key plot points and characters quickly. Focus on simplicity and a clear story arc.
Honestly, I don't know when the TYBW manga starts. But you could search manga databases or ask in manga enthusiast communities to get the details you need.