Hi J.,
First off, congratulations!
Let me first address your concerns about your house being small. Remember that up until a generation ago, it was VERY common for siblings to share bedrooms--and even beds! When I was born, I shared a room with my mom & my grandma. Later on, I shared a room with my brother.
Some children can sleep through ANYTHING, so you might be surprised at how well your daughter will sleep through the baby crying. I was 5 when my brother was born, and he was an extremely colicky baby. While the adults in the house would sometimes be up all night because of his crying, I never once remember waking up because of this.
Also, your second child may be a wonderful sleeper, and not be up all that often! Even if your daughter does wake up in the night, she can simply nap a little more during the day if need be; it doesn't sound like she is old enough to be in school yet.
When my son was born, we lived in a tiny, 1 bedroom apartment. My husband went back to work right away, so for the first several weeks, my son and I slept in the living room, he in his bassinet, and me on the futon. Maybe you and the baby can sleep in the living room at first?
As far as not being excited or happy, it will come. I think an unplanned pregnancy is always hard, especially if you had in your mind a picture of what your family and future plans were going to be, and now that's been blown out of the water. Having a child is a HUGE deal, so just know that you are not a terrible person for feeling this way, and that ANYTHING you feel right now is "normal".
My son was a planned pregnancy, and at first I was overjoyed and excited.... Then it really "hit" me and I actually spent a couple of weeks praying and hoping for a miscarriage. This admission may seem shocking to some, but I'm sharing it with you (and anyone else who reads this) because I know I'm not the only one who's ever felt this way.
A couple of years from now, how you feel right now will be a distance memory, and you won't be able to imagine life without your second child! Good luck to you, and take care!