Dress help - deep v appropriate?

So I’m from a pretty conservative/traditional Greek family. My fiancé is also Greek but his family is more modern and open minded. We just started planning our wedding for next summer and I’m looking for a dress. So far I’m obsessed with these looks. Haven’t tried anything on yet. I have a couple of questions.

1- I’m a 36dd normally, right now I’m breastfeeding so I’m about a 38ddd. What kind of bra/undergarment would I wear with these dresses? They all have a deep v neckline and are open on the back where a bra would be.

2- do you guys think it would be appropriate to wear? In church? In front of family?

3- are these dresses more for smaller chested women? Would it look too trashy since I have bigger boobs?

4- would a veil go with this style? If so, please share suggestions

Thank you!!!