I agree that a canonical question to "What is the doctrine of Trinity" can be useful in conjunction with the various questions you linked in your OP. Usually someone who doesn't quite understand the doctrine poses an objection, so giving the user a reference to both "What is the doctrine of Trinity" and existing appropriate question to address the specific objection will work very well.
To avoid duplicating the effort that the Wikipedia entry on Trinity already does very well, we can make one of the answers short and sweet targeted to new Christians (or someone new to Christianity), as opposed to the academically minded audience implied by the Wikipedia entry. That simple answer can have references to other sites for further study.
Other answers can bring different perspectives to "What is the doctrine of Trinity" as what @curiousdannii commented on: philosophical, historical, creedal exposition, analogical, Johannine perspective, counter-argument, practical, etc. to suit the angle that the questioner brings.