Is it off topic to post a fugue exposition with a question about whether the counterpoint makes any faux pas harmonically/tonally?
There's nothing wrong with a specific question about a specific piece that you are working on especially when there is an objective consensus that can be reached with the core question.
The question you posted seems fine to me, however I do feel like as a community if we can generalize questions like this it will be much more helpful to others in the future. The given question can be phrased more generally like "What are the basic areas to check for counterpoint mistake in a fugue?" Not perfect, but applicable to other people's questions in a similar vein.
Composition in general is a topic I'd love us to cover, however there are two typical pitfalls to these that questions fall into. One is that unless you are composing with a specific tangible goal in mind, there's a lot of opinion which is great for composition, but hard to keep bound in a Q&A format. The other is "what do you think" type questions which are definitively opinion based.
The question proposed does not seem like it has the two typical issues above, but I want to highlight them as things to keep aware of in the future.