Playing as the Conqueror in whether you go Westros or Essos once you convert to either the Seven or Rh'ollor you lose Visenya and are just stuck with Rhaenys.
How about making the second wife a concubine automatically? Not perfect, but you already gave the faith the possibility of having concubines...
Too clunky as many events require the seven as your religion and they would get negative opinions with those of the main seven religion due to being heretics.Targaryens practiced polygamy even after turning to the Seven. The Targaryens should adhere to a heresy of the Seven that allows polygamy. When and if the dragons die out there should be an option to convert.
Yes, but legitimacy is determined by the Sovereign, not the Church. They didn't dare speak out against Aegon or his Valyrian practices as long as he rode atop Balerion.Just legitimise the bastard. From the Targaryen point of view, the child is legitimate. From the point of view of the Faith, if it does not accept polygamy (and I don't think we know that they granted any kind of formal exception?), then the children from the other "wife" would indeed be illegitimate.