The issue with not being able to respond is most likely unrelated. If you are new to the forums, you have more stringent limitations on how often you can post. I don't know what the exact limits are (I don't believe that's public knowledge) but, if you try to respond to soon after your last post, you may see that sort of warning.
Or, the forum software is just being its usual persnickety self.
This is the only official information I can find about password parameters:
Security and your Apple ID - Apple Support
I also found this thread which is old:
maximum character length for Apple ID - Apple Community
TuringTest2 is one of the most knowledgeable people participating in these forums so I'm inclined to trust what he says.