Is there a logical size limit to enum tables
I recommend that you keep the questions in a separate table and have a FK in the answer/response table. I like my enum types to represent a well-defined and discrete concept. For example, in a order tracking system, the status of an order would be a good enum. A concept like a question does not fit that requirement. A question can have attributes (e.g is the question mandatory or optional, are the responses constrained or open-ended, etc), which in my opinion makes it something I would want to store in a table.
I can imagine a question fitting multiple categories.  If that is the case, then there should be a category table and a link table between the question table and the category table. If a question can fit only one category, then that would be a good fit for an enum column in the question table.