introducing amputated cat

Question
a little background

about 5-6 weeks ago a cat adopted me and my girlfriend.
we tried to bring him inside but to no avail.
around 2 weeks later we got home from work we both work 3rd shift and noticed he was no were to be found. i looked under an old car he was using for shelter and noticed he was a little bloody and wouldn't put any weight on his leg.
we tried to get him into a vet immediately but all were booked . my neighbor said she heard 2 cats fighting and we thought he was just into a fight , so i put him into my spare bed room. unfortunately things never got better, we finally got him to a vet and found out he was SHOT . we were referred to an orthopedic surgeon .
we decided amputation was the best route.

now the question
i have 2 female cats and 1 male cat already - all are fixed even the amputee (he was somebodys pet at one time)
my cats seem to be used to him. he on the other hand  hisses at them through the door and when i had him in a carrier. we were thinking of getting a dog kennel and putting a roof on it for him because he loves outside. but that don't solve the cold winters here in Pennsylvania i know i can never let him roam free due to the amount of pricks with guns around here any ideas on introducing them.

Answer
Hi
firstly can i how awful that someone shot a cat. I don't think i will ever understand some human beings.

Any way onto your question. i get asked this sort of question a lot and so i have written a page about it on my website. Here is the link

/introducing-cats.html

I hope it helps to settle your new cat into the home.

Thank goodness for people like you.

best wishes
Kate