Every two to three days- for me that would be a big worry as on average cats eat about 2-4 pouches of food a day and graze on dry food and their water needs to be changed daily. If your neighbour is only coming every two to three days- what is your cat eating on those other days? I guess you must be leaving lots of dry food for your cat, but ideally they need wet food as well as it’s good for their bladders. Water should also be fresh. Hopefully your cat has access to come and go through a cat flap so they’re getting fresh air etc. The question about a play mate- really depends on the individual cat’s personality. Some cats are quite happy on their own, but if they’re clingy when you return they may be lonely. If you can set up little things in the home like boxes to play with and treats hidden in places, it will keep you cat busy and happy for a while. (More difficult over a long period of time as your cat may fin everything in one day, but if you put something different in every room they will love exploring it).