Good on you for wanting to help. Most rescues will provide the things you will need, but will ask that you have a way of isolating, I took in 3 cats from a home environment last weekend that had both fleas and worms, so unless they have already been at the rescue and done, you cant guarantee little things like that, much less anything like catflu. I isolate for a fortnight, and even then they only get limited time out, partly cos it is my cat's house, and they dont always want to be bothered by all these newcomers.
There is no way of knowing how long they will be with you, I have had cats that I thought would be short term and snapped up quickly tak ages to rehome, and vice versa. It might be worth offering to do a CC page for the rescue you help, as htey can be a big help in rehoming. You also need to be able to dedicate a decent amount of time each day to them, and to all the extra cleaning it will create. i am no help with not getting upset I'm afriad, as it doesn't bother letting me know - I am always happy with the home they are going to, and there is always more needy cats that will benefit from me letting one go. I agree with Angie's last sentence, I am 'Auntie Des' to fosters rather than 'Mum', and them being separate does help a lot, the long termers who are integrated have been harder to let go.
