1. Does Bella really understand all that she will give up in becoming immortal? Do you think her understanding is limited by her age, life experience, or something else?
I will admit that at first, I was hesitant to accept Bella's firm decision to CHOOSE to become a vampire. Sometimes it seemed hasty, and I could see where Rosalie was coming from as to all the things Bella would have to give up. I love the things about Bella's character that are obviously flawed and human. But on the other, stronger side of the argument: Bella found her true love in Edward. Not just a teenage crush or a summer fling, but her one, true, soul-mate love and destiny. Coming from first hand experience I know I would never want to part with mine, so I know exactly what and how she was thinking. In the books, Bella's mom is always joking that she, "...was born 35 years old and got more middle-aged each year." Bella is independent, can take care of herself (except for the accident-prone moments, but other than that I think she proved herself quite capable), and has never felt like she really fits in (besides Jacob, the Cullens, etc.) so I don't think age had anything to do with it. Bella sees the Cullens close up from Twilight all the way through Breaking Dawn, so I believe that she had a pretty detailed idea of what she would be getting herself into, and in the end, she gained so much more.
2. What do you think Emmett and Jasper were going to do for Edward's bachelor party? Was Jasper telling the truth?
This is a really great question! I have wondered about this since I read the fourth book
I don't think Jasper was lying...but I definitely think he was omitting some of the events they had lined up! I'm sure it was the typical male-wreaking-havoc...vampire style. I agree with an earlier post that I just couldn't picture Edward in a strip club! Too much of a gentleman. I could definitely picture them going for an insane drive/racing their cars, etc...something ridiculously dangerous but loads of fun for an immortal
3. Tanya made a play for Edward long ago. We don't know much about Tanya, but we know quite a bit about Edward. Why do you think he turned her down?
I'm going to have to agree with a majority of the posts I've already seen. Edward waited a century for Bella, who is such a unique, amazing, one-of-a-kind girl. Just because Tanya is a gorgeous vampire, doesn't mean she has what it takes to win Edward's heart. And as someone already stated, why would Edward - old-fashioned gentleman - want a companion who has seduced many men before him? He had never given his heart (or virginity, for that matter) to anyone, so I'm sure the last person he'd want to give that to is Tanya, who simply just wasn't the one and tried too hard for his affection. Even Bella as a vampire compared to Tanya yields them as definite opposites on many levels. Edward loves the fact that he takes care of Bella, and looks after her, and that she isn't afraid of him for what he is. To him, Bella is his most precious possession. If Edward loves Bella, and Bella and Tanya are nothing alike, then it is pretty easy to figure out why he didn't like Tanya. It makes me wonder how many times Edward has had passes made on him by females - human or vampire - and if that affected his thoughts on love.
4. About Immortal children. At what age or developmental stage would the Volturi allow them to be created? A two-year-old usually understands the word no, but evidently that wasn't enough. How would they determine if the child could "keep the secret"? What would the determining test(s) be?
It seems as if the Volturi made certain acceptions when the outcome was in their favor (Jane and Alec, for example.) But although Jane and Alec were of the youngest vampires, they were obviously still capable of a complicated thought process, communication, etc. Even though Renesmee is not an immortal child, she turned out a certain way because of who she was raised by. When the immortal children were created, their purpose was to be a part of a killing army. I agree that the younger the creation, the harder it might be to control. But at the same time, if an immortal child was created in a supportive, loving environment such as the Cullen family - would it have a different outcome than the immortal children created for the wars? YES, most definitely.
Different people mature and grow at different rates, and age is only a number. But at the same time, there are certain things you just couldn't expect a 5-year-old to understand or be held responsible for. It seems to me that possibly the age of pre-teen, where adult-like behavior and ways of thinking become more prevalent, would be a more suitable age minimum for creating vampires, in this case.