Binary log backups in MySQL
log-slave-updates=true 


should be true on both masters. Because if both masters are accepting updates then the other passive master has to be able to update itself.
You can take backups of the bin logs whenever you want. 
As to other options, I use the MIXED option for the binglog_format to allow for ROW based or STATEMENT based updates 

binlog_format       = MIXED


This is because STATEMENT based replication doesn't cover all updates. But STATEMENT based replication is faster. With MIXED MySQL can switch for you when appropriate.