P.,
Let me assure you that your daughter is perfectly normal. I teach a sibling class at a local hospital. I strongly recommend you call the hospital where you'll deliver and ask about a sibling class. If they don't have one, they'll recommend a hospital that does (most major hospitals have them).
Here's what I tell parents with this concern. Remember that your daughter has had just you and her father for her ENTIRE life and now your tummy is big and everyone's excited and talking about a new baby. Her world is about to be ROCKED!
Keeping that in mind, treat her with kindness and compassion and at the same time, set limits and boundaries. I set just a few rules for my daughter when I had her sister. Keep it simple, be consistent, and be loving.
One more thing, perhaps you and your husband can set some limits and boundaries around your disagreements. Keep that simple too! You can have a hand signal like putting your hand up and say "stop" when an argument is getting heated in front of your child. Children learn how to treat others (including us) by what WE model for them. TV is not the culprit. It's us. And you, as her mother, are the most powerful role model in her life. Your husband is the role model for who to marry. Keeping that in mind, you two should act accordingly. No one is perfect and your children don't need you to be. They do need to see examples of people working it out with loving kindness most of the time.
Research dictates that a three-year span between siblings is ideal. So, you've got that part right!
Good luck and keep the questions coming!