Ideally it would be nice for our pets to have a buddy. They are usually left alone everyday so having a buddy to cuddle up with would be great. There is a chance that they may not get along but more than likely they will learn to accept each other especially if you work hard at properly introducing them. I introduced two dogs and a cat to each other and I'm not saying it was easy but in the end everybody gets along and they even all curl up together to nap on occasion. As long as you can give them their separate space when/if needed and you are prepared to double your vet and food bills you should be just fine. You might also want to consider the litterbox situation. I only have one cat and one box but my friend has two cats and she tells me she needs three boxes as they need to each have their own as well as an extra? Not sure about that part but maybe someone else here that has multiple cats can confirm that or not?
I would keep them separated in the beginning if you go out just in case there is a "dispute"