Congrats Kittybeep,
That's why I couldn't volunteer at a shelter - I'd be pulling into the driveway surrounded by a sea of wagging tails!
We have saved a couple of cats from death row - both adult cats.
They were harder to settle into the house as our existing cat felt threatened with a new adult around - territorial and jealousy issues. We took it slowly - kept the new cat confined in one room initially and slowly arranged the "introduction"...
Our current tabby had a rocky start - our Siamese (probably defensively) attacked him - it was more noise than anything else but it frightened us...it took months for them to settle into an uneasy arrangement where they "tolerated" each other. We gave the Siamese lots of attention - reassuring her all was well. We watched them closely and didn't leave them alone together for weeks.
The last year they have spent a fair bit of time at the cattery together and it's clearly been a bonding experience - they'll even curl up together in the same chair! They still rumble from time to time but not as often - they definitely have a sister-brother relationship.
Good luck - hope it all goes well.
PS Sometimes a cat will start to spray if it feels upset or its territory is threatened - the vet gave us some pheromone spray which was really helpful - seemed to calm them down - also, its a good idea to have some cat nip in the house...
