Excellent choice!
Believe it or not, porygon (and its evolutions) are actually some of the easiest pokémon to care for. A porygon (or its evolutions) doesn’t actually need much in the way of food, and water should be kept to an extreme minimal anyway (as it doesn’t interact well with its electronic-digital nature). It can eat if they choose to, so it wouldn’t hurt to offer the option. Should you choose to do this, porygon and its evolutions will literally eat anything you tell them is food, and they will do so happily. The same sort of kibble you give the rest of your team or small, extra portions of whatever your other teammates will eat should do. Alternatively, you can offer an extra portion of your meals whenever your porygon seems interested. Remember, the main point is feeding porygon only if it seems interested, not because it needs to, as it really gains no nutritional value from what it eats. On the other hand, your porygon will likely engage in mirroring, or the act of mimicking the humans or pokémon around them in order to understand and bond with them.
In truth, what a porygon needs more than anything is a computer. That’s where most of your maintenance will occur. Porygon aren’t tied to any specific computer, so you won’t have to worry about, say, needing to transfer your porygon whenever you buy a new computer. However, it’s always a good idea to start out with something sturdy, quick, and equipped with a considerable amount of RAM and powerful antivirus and anti-malware software. A connection to the internet is also highly recommended to allow your porygon to move from one device to the next without having to exit into the real world. (I would also recommend coupling other devices, such as your pokégear, pokénav, phone, or so forth, with your computer from time to time to allow your porygon to jump from something you own to another piece of personal tech.)
As a note, whether you want a laptop or a desktop is entirely up to you. Desktop computers tend to be sturdier and have more power, but laptops are portable, allowing your porygon to have a refuge no matter where you go. Thus, if you tend to stay at home, consider a desktop, but if you frequently travel, a laptop should do.
That said, once you get this computer, power it on for at least a few hours every day. Encourage your porygon to enter your computer at least once a day to recharge, which is its equivalent to eating. During this time, run your antivirus and/or anti-malware software to “groom” your porygon. If you have a poké ball transporter and a home connection to the storage system, I would also recommend uploading your porygon’s poké ball and running the system’s backup software. This will also pull a backup from your porygon, even if it’s not within the storage system itself.
Also, don’t worry about your porygon wandering around the internet. Porygon and porygon2 are extremely obedient, and it’s unlikely that they’ll wander too far without you. This is also tied into their care regarding play and training. Porygon need very minimal training, not only because they don’t often display behavior that needs to be trained but also because their bodies don’t require much exercise. The only thing you’ll need to be concerned about is really target practice; it’s essential that you hone your porygon’s aim and accuracy especially, as these need to be calibrated over time and are key to their beam attacks. As for play, porygon and porygon2 are fantastically intelligent but also extremely agreeable, and they can get the psychological relief they need from playing any sort of game with you, from fetch to chess. You can even open up a creativity program such as Photoshop and let your porygon play through artistically expressing itself. (You won’t believe how much art on the internet was actually created by porygon. It’s quite fascinating, really.)
Of course, this leads to the metaphorical donphan in the room: porygon-z. Porygon-z, being a pokémon with rather unconventional origins, has a risk of tripping your antivirus software or negatively affecting any computer it touches. For this reason, it’s important for you to be extremely careful when it comes to handling its maintenance and its training. Don’t run your antivirus software on your porygon-z, but if you absolutely must, make sure your porygon-z is whitelisted. You should still run the backup, however; rest assured the system administrators have taken porygon-z’s unusual nature when designing the backup system.
So really, your biggest concern is training, as porygon-z gains more of a personality and thus may pick up several bad habits. Luckily, it’s not as bad as many experts will lead you to believe. In truth, the only reason why porygon-z seems like an insurmountable challenge is because trainers are used to training porygon and porygon2, both of which are among the easiest pokémon to train (in terms of behavior, anyway). With that in mind, porygon-z is really just about as easy to train as any other pokémon; it’s just that you may need to deal with its newfound curiosity. Keep an eye on it and have patience with everything it does. Teach it the difference between exploring its world safely and doing so impulsively or dangerously, and don’t be afraid to use positive reinforcement to help it understand right from wrong.
Best of luck!