Upvote:4
I did this when I was in the UK. I can tell you from my experience. I believe it's going to be almost the same as the consulate in the US.
I used Booking.com and it's enough to show that you have confirmation of accommodation.
I used to use Hostelworld.com as a confirmation as well and it worked for me. However, the email had my name on it.
I used to use AirBnb and it also worked as a confirmation.
I have never done any couchsurfing so I can't really provide and details.
Email from your friend wouldn't count as confirmation of accommodation as far as I'm aware. Having said that, I used to have my friend wrote me a letter stating that I'll be staying with him from ... to ... and I attach his copy of passport and it also worked.
I suggest you call the German embassy in SFO to confirm about all of this again. I did the same when I was applying in London and they gave me all the details how they want the letters to be.