1. It uses the tags system for stable references as originally devised for the Stacks project by Cathy O’Neil.
This means that if you reference a tag in the Stacks project or Kerodon, you should make sure to specify which of these two you are referring to (if you use the “cite” links in either project and copy-paste from there this will work fine). All of the references I’ve seen to the Stacks project already do this, so I am not worried.
Some of the work done for this by Pieter Belmans will also benefit the Stacks project (this will probably be mostly invisible to the user though).
3. It has a comment system, so please go over there and leave mathematical comments!
4. The mathematics in Kerodon is written and copyrighted by Jacob Lurie.
This is a difference in philosophy: (a) the contributors to the Stacks project collaboratively own the Stacks project and (b) you can directly access the underlying latex files to make changes to submit to the maintainer (me).
5. Currently the pdf version of Kerodon has 85 pages.
The plan is to add more over time. As you can see, the current material covers a tiny fraction of Jacob’s book entitled “Higher Topos Theory”. If you want to know more about what is planned in Kerodon, you’ll have to ask him. But for now, I am kind of taking this opportunity to read Kerodon the way you would read a webcomic. As new material gets added I will head over there and read it. I hope you will enjoy it as well.