Ask HN: The real story behind your first startup?

Hi. I know this might seem close to stupid, but I would like to submit one of my ideas to YC this year, and I would like to know from others that have been there how is it like? What do you do when you get the email that says your good to go? (if you are not in USA - we need to plan our trip some time before in order to get flight tickets) I have read on YC that you can stay there in the YC campus (or what was the name), do you have to pay anything for accommodation? We have a limited budged that's way we would like to know what kinds of expenses we should take in consideration? We are 2 members, if this helps in any way.

I am asking this in order for us to have this little things (that usually can become frustrating) out of our way so that we can focus on the real issue, the project.

Thank you very much