1. The VA have been working for Bethesda for nearly 2 years. And will likely keep just keep working for them as the DLC comes out.
This is a AAA game with a AAA budget so they are not going to skimp on the voice acting.
F3 had 40K lines of dialog, FONV had 65K lines of dialog.
Fallout 4 has 26 K lines of dialog for just the male and female protagonists.
You don't need 13K lines of dialog for the protagonist if you are skimping on the voiced dialog from the NPCs.
My bet is Fallout 4 will have well over 100K lines of dialog.
I mean if nothing else there will be more people to talk to.
2. I don't remember what the average number of dialog choices in a F3 or FONV conversation, but not very many of them were over four.
And it is natural that if we ask Godsworth one question, we would start asking more questions. I expect once we asked the first question, we would be given the chance to ask more questions or to go back to the top.
3. Guess we will have to wait for the game to actually come out.