@eesty what is the company policy?
It seems it would probably be cheaper to not migrate from NodeBB but have us host it for you as a vendor.
That is what happened to the FusionAuth forum 🙂
Maybe you can check nodebb-plugin-mentions, since is in that plugin where the @user-slug is searched and processed in order to compose de link to the user profile in the post message.
In that plugin i suppose a search is made in order to obtain the user id, you could obtain user avatar the same way.