Hi, I am in this exact situation now, and have been searching for information too. I have a 14 year old male cat, and yesterday have 'fostered' a kitten found abandoned near us, which appears to be 6 to 8 weeks old. We also have a 10 year old dog.
The dog is fine with it, the kitten is not phased by either the dog or older cat, but my older cat hissed and growled at the kitten when face to face. From what I have read this is normal and we should keep them apart for a few days getting them used to each other's noise and smell etc, then gradually introduce in short bursts. Our old boy hissed at DH last night, which has really unsettled us as he is the most wonderful loving cat usually and I really can't risk upsetting him permanently. This morning though he is back to his usual loving self, and I am keeping them apart for now.
I don't know if it will work out, but if things are not good in a few days we will have to find a new owner for kitten :(
I hope not as this little kitten needs a home, is covered in ticks, starving hungry and not cared for (which we are now sorting out), and I have always wanted a kitten!
Sorry if it doesn't answer your question, but I am keeping my fingers crossed things work out, as I understand they usually do, but it can take time.