Chill_ean_GUY
I would go with the second option since this is your story now and should make some minor changes. Last chapter had him be transported when he was coming back from a war campaign unlike last time which had him transported and like a castle or something so it would make sense that he would have more soldiers with him this time.
Having MC be met by Aegon during his war with Volantis (before the conquest) would give you the most flexibility with choosing what Old Elites you assist/curry favor with and which you root out. Being apart of the conquest given the amount of war, politicking and systematizing the Prussians did would mean MC could have maximal impact while you can get rid of houses you don’t like/threats to Targaryean rule and the German’s army’s livelihood
If MC were to incorporate Germanic/Norse mythology into Christianity he could pitch it to his soldiers as Germanifying a Semitic religion forced onto them by the Romans while also appearing similar enough to both the faith of the 7 and the old Gods as not to rock the boat with the commoners of Westeros