b) "must we finish a whole branch after starting it?"
Yes, please. Because we have insufficient tools right now for showing where people are, and because the communication methods we have are also limited, reapgrowing/SCing will currently work best if everyone can generally trust that when a person says they're starting work on a given branch, they'll be there for a bit.
k) "can anyone claim multiple branches at a time?"
Well... yes and no. I mean, "branches" is a loose concept because one branch will usually split into several more before it nubs, depending on the cell's morphology. So if you claim one branch you are implicitly claiming its child branches. At the same time, please do not claim simultaneous multiple branches in the sense of branches that all originate at the CB.
from this i take it that you should not start reapgrowing unless you have at least 4-5 hours to play to be able to finish several hundred cubes so you will be able to finish the branch, personally i prefer to just scroll at the chatlog and see if the earlier reaper of a branch have been active reaping for the last timeperiod and if not i have felt free to take over that branch in the past.
and good with the clarification that we do not need to reap every cube on a branch.