Welcome. And my sincerest sympathies in your loss.

As for the boy kitty, his actions don't need to all stem from the same problems. The following you around, and need for attention is probably due to the loss of his cat companion. The eating of canned food could be a medical reason. (Has he seen a vet recently?) Things like bad teeth/gums might make him choose the soft food over the hard food, for example. And at 13, even though not "ancient" is OLD, and the onset of senility is always a possibility, the loss of some sight might make getting used to a new home a bit harder......etc.

Try hard to give him as set of a schecule as possible and keep whatever you can from his old routines before the move. Have him get a senior check up at your vet to make sure his body is functioning properly and then just give him time.

A little cat companion might be good for him, but I would never recommend a kitten. At 13, that might cause too much stress on him. (Kittens can sure pest the heck out of a cat, and a lot of adults don't have the patience.) A young adult with the reputaion of liking other cats without dominating them, might be just what he needs.