Welcome to Cake, @RandallSnyderJr!
We don't currently have any upper limit on the total number of topics a user may follow. What you probably ran into was a limit on the number of topics a user may follow within one minute.
Currently, that limit is 60 follows per minute. So in order to hit the limit, you'd need to follow at least one topic per second for 60 seconds. But if you wait another minute, the limit will be lifted and you'll be able to follow more topics.
The purpose of this limit is purely technical: it's meant to protect our systems against possible abuse. If we didn't impose a limit, then a malicious person might be able to overwhelm Cake's servers by writing an automated tool that just constantly followed and unfollowed thousands of topics. Our goal definitely isn't to prevent users from legitimately following topics, so I'm sorry you ran into that limitation.