we didnt set out to have 5 cats... God blessed us with the first, Pumpkin,(solid balck, short hair) whom my husband said would "NEVER" come in the house, (5 yrs ago) then we added Chloe, a long haired persian, also black and white, then P.J. a huge maine coon, black and white and the biggest pet bomb on earth... after that DH said NO MORE.... well he was cleaning the auto's, and low and behold, Lemony Sneakers found him. that made 4 inside, well it seems that you can get literally EVERYTHING at walmart, including a kitten, Shady Sage being our last addition.
all were strays and needing a home, and well we needed the kittens i guess.
we have since founds more strays, or they have always found us, (McFlurry, Smoky Sable) but somehow they were not meant for us, and we have always found a home for all of them.
i think that you will know how many is good for you if you listen to your inner voice.
5 cats are expensive!, and they are exclusively indoors, and Yes! nothing is sacred anymore, they can and do get into everything!, and they can make you crazy from time to time,
but when i have had a very long and hard day, and i think i simply dont have a friend left in the world, i can pull into the drive way, the house pitch black, and hear them 'kerplunk' down from their sleeping spots and they are ALWAYS waiting to greet me and they always want to hear about my day... that makes it all worthwhile...
stace

I would wait and let your older cat enjoy his last 5 years without a kitten.

I adopted the foster kitten (Puja) I was caring for. Even though my 5 year old cat Sofie seemed to accept the kitten while I was raising her, she is not so happy now, and I regret it. Sofie would be happier as an only cat.

I adopted two one year old siblings when my old girl was 16. Although there was a rough transition period, I swear the two young ones kept the old one going--she lived to the ripe old age of 20. And now I have a second generation of cats who keep each other company and entertain each other. Basil and Sally are now 9. I'd do it again in a heartbeat.

I had an elderly cat (13), Nikki, who at the time was an only cat. My sister's cat had kittens and she said I just had to come see them. I didn't want to (because I knew I would want one) and Nikki seemed fine by herself. Of course I broke down and went to see the kittens, and fell in love with the cutest orange ball of fur. I brought Toby home at 8 weeks and Nikki took to him right away. She had never had a litter but took to Toby so much that she let him "nurse" from her. He was weaned but for some reason looked upon her as his new mom. This nursing bit lasted until he was about a year old [but that's another story ;>)].

When Toby was about a year to a year and a half, every day when I would come home from work I would find the blankets on my bed laying on the floor. No pee or poop or anything, just blankets on the floor. I used to think, "oh, isn't that cute." Finally it dawned on me "he's bored!" Here was this young guy who wanted to play and wrestle, and all Nikki wanted to do was sleep and be the princess. I ended up adopting another kitten, Timmy, and of course Toby hated him - for about the first 3 days. They eventually became best buddies, and left Nikki alone to sleep. And guess what? Once I adopted Timmy, Toby stopped dragging the blankets on my bed off to the floor! He really was bored! What ended up happening was that both Toby and Timmy became very protective of Nikki. Nikki had a heating pad that she would sleep on, and if Toby was on it, when she hopped up on the couch, he would immediately move to let her have it. Toby and Timmy would even lay beside her - one on each side - to snuggle with her and keep her old bones warm. They looked out and took very good care of her. She ended up living to a ripe old age of 19. When she passed away, Toby and Timmy mourned big time. I haven't gotten a 3rd cat, but in my case, having 3 worked out beautifully.