The cabins and interiors of the boats are air conditioned.
I don't remember for sure, but something tells me the beds could not be pushed together.
Just about all of the cabins have a door from an interior corridor and one to the outside deck. We were on the American Queen. There were chairs right outside the French doors. I only saw a couple of cabins with private verandas.
I don't think steamboatin' can easily compare with cruise lines. Even the American Queen, which was the largest of their boats, only held about 400 passengers. Things are definitely laid back and friendly. It's an experience all in itself.
I am sure most TA's can handle the booking for you.