Hi Bas, really glad this was helpful for you! I will be updating it shortly to include some other troubleshooting and extra commands I have used to overcome errors I have hit.
Which part are you referring to that the step is missing in official docs and . that they say you should not commit to local horizon repo in devstack? I personally do not do that and am talking about connecting devstack on a VM to my local horizon environment where I commit to and submit reviews to upstream gerrit.
WRT changing the endpoint IP address, there is a comment on that suggesting that as of 2018, this does not work anymore so just a warning that the next stable release might cut out that functionality. I have a static IP for my VM but in the past have not set that up and just survive with ./unstack.sh and ./stack.sh as frustrating as that can be, although VM snapshots can help there.
Hope that helps!