At this point, probably most user had already run ./autogen.sh. But calling ./autogen.sh twice is non problematic and better twice than never.

ACK.

This is also a more complicated section of the doc, so perhaps the presumption is of an advanced user.

It just depends on how you think of docs and their purpose. I always try to write them as if the reader is typing the commands without knowing why. A very good doc will get the job done in that case too.

It's just an illustration how to point bitcoin's configure at your own BDB - not a general description how to do the autotools configure process - that should have been described earlier, so it may be better to refer back
But no problem with this change...

ACK. Please squash your commits.

ACK after squashing.

sorry ... I tried

git rebase -i HEAD~2 
git push origin master --force

Do I have to resubmit the PR now?

Please don't resubmit/re-create the PR.
Just use git rebase -i HEAD~2, pick (p) the older commit and squash (s) the newer commit, ... than force push again.

@jonasschnelli very good thank you.