As long as you don't submit the hidden custom page to Google. Nothing to worry. It's a very simple practice as in Wordpress.com blogs. Only you know the existence of the that custom page, and you don't even need to 301 redirect.
However you should check your sitemap (generated by Sitemap plugin) to see if there are some undesirable URLS. Who knows!
The real problem is the ugly Category urls. Yoursite.com/questions/automobile and Yoursite.com/tema/automobile coexist. Yoursite.com/questions/automobile and Yoursite.com/automobile are almost identical most of the time. But the important thing is that it's very not handy for users to browse old questions, because they will have to read the first page again.
After spending sometimes with Q2A, I decide not to use Categories. Big sites like Stackoverflow or Quora don't use categories, only tags.
If you check out the profile of jair. He did write a plugin to add pagination to categories. Pay him if you want. https://www.question2answer.org/qa/user/jair