I also recently adopted a stray and the vet said that it is best to keep the cat indoors for at least 4 to 6 weeks. The cat was very thin and full of worms and fleas. She is now a happy, healthy cat and my other cats love her. It took a while for them to accept her but they are now best friends. It is best to let the new kitty settle in before introducing it to your other cats. Give the new kitty its own litter tray and food bowls, even after introducing it. My vet also told me to buy new blankets for all my cats and after a week or two I had to swop the blankets around, this really helped to get my other cats to get used to her smell and she got used to theirs. I also left her room open, but divided it with mesh so that the cats could see each other without any harm. The most important thing is to have lots of patience and to reassure your other cats that they are not being replaced. Good luck