Full Database backup internals
I would try to answer the question as whole. Yes I believe book has some discrepancy as far as my knowledge goes.

One thing for sure is that the backup explanation pic mentioned in the book has some typos. It forgot to use word commit and instead continued with word starts. Like Xact A Starts is a transaction that started much before backup and somewhere at last it committed and still the pic shows Xact S starts it should be Xact A commits similarly for transaction B. This is what you mentioned in point 3



Now let me give you very clean definition of what is MIN LSN here. The MIN LSN would be MINIMUM of (Oldest active transaction which is when transaction C starts , LSN when backup started and checkpoint was fired, in this case red line showing checkpoint). This is always how minimum LSN in case of backup would be calculated. Please note Transaction A started before backup but committed before backup ends so it would not be oldest active transaction and also as per backup operation the pages were read so this would not be the oldest active transaction.

Now let us go to definitions

Backup Start LSN: This is basically "Checkpoint LSN"( As mentioned by Paul Randal in Understanding SQL Server Backups) this is recorded when backup starts and checkpoint is fired.

Backup End LSN: This is basically reading the transaction log again and recording 2 things 


The LSN of oldest active transaction.
The LSN when backup operation started, For this I am not sure whether this happens or not IMHO this should be same as Checkpoint LSN or Backup start LSN but may be SQL Server is doing this 2nd time to confirm. I believe it does only what I have mentioned in point 1. 


Minimum LSN: The would be minimum of ( LSN of oldest active transaction, Checkpoint/backup start LSN ). The definition in the BOOK is little bit confusing.