I dont know how the ceremony goes but do the couple stand/sit in chairs in picture 2/3? I only shoot jewish weddings and while Ive shot 2 christian wedding, this looks different so asking.
we do not have the same gear but its
very clear how Id shoot this here. 2 light stands 12' high flashes running at 1/32-1/16 power. no battery packs needed. iso 3200 no problem at all. but im FF and here is the wall you will hit since youre DX. it seems you want to keep iso low and this will be a mistake. this is not film days and you should release yourself from the though of shooting at 400 iso.
the point is either you up the iso (youre not comfortable with), up the light in the room (not possible) or add tons of flash. but be aware, your flash will work very hard with low iso and recycling fast enough for multiple shots. you may miss critical shots. the answer? more than 1 flash on the camera.
heres how Id shot a typical situation like this and I do all the time.
2 light stand in the back raised high behind the seats. aimed towards the area between right after the 1st light in the picture (closest to us in the image-back of the room) it will bounce a bit to the back and mostly push it a bit more to the front. these 2 with one flash on the body as well. I now shoot in manual flash mode on camera. ttl may be better for you but you will need to use FEC