Do you think Varys had any knowledge of Doran’s plans? I may have missed any textual clues of that, if they do exist.

Good question. He might have, he was certainly paying attention to Viserys and Dany from an early age, and Magister Illyrio was in touch with the Golden Company before he was hosting them, so I wouldn’t be surprised if he was paying attention to their political support in Essos.