I recently found this graphic in this post.
The problem is that this post is quite old. So I would like to know if this graphic and that post are still valid. Especially since it’s been a long time and many other updates might have affected it in some way.
For example, this post came out recently and I don’t know if it affected it at all.
Scripts located in ReplicatedFirst MUST use WaitForChild(), since they load first before the game even loads, while scripts that are outside ReplicatedFirst should not use WaitForChild() UNLESS that part is going to be created later by a server script, etc
And the same goes for server scripts, you shouldn’t use WaitForChild() unless the object is not created yet (Will be created later by a script)
Slightly disagree, the diagram in the OP is correct—LocalScripts might start running before certain parts (like the character) are replicated, so WaitForChild is still necessary.
I would say so, the update post doesn’t affect the order of these steps, just the order of individual siblings.
Also if you turn on game streaming then all bets are off as to what’s on the client and what’s not 
Sorry I forgot to mention the character, it is still considered something that loads in after the game runs though
