Yeah, a negative experience could affect the potential relationship between the two, but it can still be worked out. I would still suggest to follow my advice, especially making sure your cat doesn't see the new one for a period of time—they need to be acquainted, so having your cat stay in the place you keep the new one so that it can get used to the scent is a great way to "stimulate" a bond between them. It takes time, but works. Do keep in mind that not all cats necessarily become friends, but they will at least tolerate each other.
Remember that your house has been your cat's territory, and the addition of a new one will undoubtedly put a strain on it.
In regards to the bowl, don't place it directly behind the door, it's preferable to place the bowl at a distance and move it closer to the door each day.
Like I said, cats are fickle; one alone can be quite a hassle, two are a chore, so if you believe it would be best to find the cat a new home, please do.