All I know, is that in my heart, I really have to give this a try.
Then that is all that matters.

My very first piece of advice to you.....do not allow hissing to bother you. Hissing and growling are a warning to others to "stay away, I am not happy". BUT it is prefectly normal and to be expected.

Also remember that chasing, in and of itself, is not a bad thing. A cat will chase off an intruder and the NEW cat will be trying to protect an amount of territory. Only when the chase ends in an all out brawl OR if one party begins to be terrorized into hiding all the time, would I worry.

oops....sorry for the unsolisited advice.