It's up to you and your household. I have two dogs...getting any more animals would be too much for me because hubby and I want to have kids in the near future. If we didn't want kids...I would definitly get some more animals.
I wish I would have gotten our pups at the same time. We got one, and when she was about a yr old we got another. I think it would have been better for them if we got them at the same time...harder for me...but whatever.
There's also a lady here (me) who got 2 shelter puppies (Cara and Mia) at the same time and found the experience to be the joy of her life! I would do it again in a heartbeat!
Getting a kitten at the same time would be too much for some, but since I don't work, I think I could do it. And if they're raised together, it's likely you won't have problems with socializing them to each other later. Bringing a baby kitten into a household with dogs could create issues.
When I 1st joined my obedience club 16 yrs ago one of the junior instructors had adopted litter mates. She was warned before hand that it wasn't a wise thing to do. She wouldn't listen & got them anyway. She said she knew what every one said was right & would never do it again.
The thing is to do things with them separately so they don't become so focused on each other & not the owners. So at least twice a week give them separate walks & training. I've seen it time & time again at my club when ppl adopt 2 puppies or dogs from shelters at the same time. During a class they are whining to be with each other
& won't concentrate on the one trying to train them.
I read an article on the net last year that talked about adopting dogs & it said that if you have a large dog to wait (now I can't remember which way it went with regards to large & small dogs) 2 yrs between & if you have a small dog to wait 4 yrs. Or it could be the other way around.