I'm currently making a Scratch Bot that replies to people if they comment on the bot's profile. I don't want to get banned so I'm asking beforehand.

After a quick read through both the Community Guidelines and the Terms of Use, it appears that there is nothing in there that would be against a chat bot… Except one thing: Spamming. There is a chance that creating a bot for a specific Scratch profile could count as spam, as it immediately replies to people on the profile (presumably with very similar messages based on what is said). If this is the case, before you take further action, I'd recommend asking one of the Scratch Team members on their profile to see if this would be allowed or not.

The rule for impersonation or trying to trick the community might be broken as well, but from what I could see it doesn't seem that it should also come into effect.

Yes, this is not allowed.

I wouldn't think making a bot is allowed in most cases. You'd have to ask a Scratch Team member what cases these are, though.

By my knowledge there isn't any rules stating anything about bots tbh.. you should ask the ST if you're unsure..