Man that is a hard one. That is a lot of choices!
Living Room- I personally did one of my births in the living room (and might need to do this one there if we don't move before hand) and I wasn't fond of the lack of privacy. Kids were running through and all guests were pretty much right there. I like my distance. I enjoyed the bedroom better.
In regards to movies...could maybe you move the movie player to a different room or maybe set her up with a laptop with movies or games? As far as kitchen noise goes...just tell guests not to be messing around in the kitchen.
Porch- It sounds like it could be a great if all of the variables lined up right....but to me there are too many variables. You don't know time of birth, so you don't know if weather is going to be acceptable. And mosquitoes would be a huge bother. Plus I don't know about where you live, but where I live I couldn't get away with it because of neighbors. They would either be able to see or hear and I wouldn't like that.
Cottage- This sounds like a great idea. You could have it all set up ahead of time and not be in your way (one of the biggest annoyances I have with homebirth). In regards to bathrooms.....I personally don't find myself getting up to go to the bathroom during birthing. Now I will say that while birthing, things tend to happen, but that wouldn't be changed by the presence of a toilet unless I was birthing over a toilet! Outside of guests needing a potty, I don't think I would worry about it....and they can run to the house if needed. If you really want a toilet available, you could get into camping toilets. You could buy one or make one.
In regards to heat, I know with me personally with all of my water births I was more cold because the water had a hard time staying up to the temp I wanted. My last delivery I was shaking because it was so cold and that was even with them panning in hot water from the stove occasionally. And if you get hot, they can add cool water or you could have them spritz you or give you cool cloth. But with me, warm was my friend. =) Also, if the cottage has windows you could open them and get some breeze. You could also have fans or perhaps even invest in a window ac unit or maybe borrow one if you know someone that has one that they don't use. Or you could make a few "hillbilly air conditioners".