Actually, porygon are some of the easiest pokémon to care for because they don’t need much at all. At the very basic, they need a reliable and well-maintained computer or two, not to serve as housing but instead as a gateway to and from a digital world. They essentially live in the cloud, so as long as you have something that connects to a digital network (even your pokédex will do—just not a rotomdex, as porygon’s passage to and from the digital side of things may be awkward for both parties), your porygon will be perfectly happy. In other words, get a computer, an internet connection, and some decent antivirus software and avoid shady websites, and you should be fine.
Everything else is optional, more or less. Porygon don’t need to eat or sleep, but they can do either. (They have no consistent food preferences, so feel free to experiment until you find something your porygon likes.) They prefer games that involve their trainers (such as chess), and while they don’t need exercise in the same way other pokémon with natural, physical bodies do, it’s a good idea to engage in target practice once a day to hone their beam skills.
Maintenance is likewise very easy. Simply have your porygon enter a computer and run a porygon maintenance app. I personally recommend the one created by Meowthware Bytes, as it’s thorough and highly reliable. Just be sure to download it from the company’s actual website, as there are fake versions out there. This bit of software will not only run a basic health checkup and remove corruptions, but it will also run your porygon’s internal backup system for a complete maintenance session. This should be done at least once a week.
Also, whatever you do, don’t modify your porygon’s code, no matter how well-versed in computers you think you are. In the porygon stage, you could actually kill it this way. (The porygon2 stage may risk evolution, which is only a negative thing if you’re not prepared for porygon-z’s capricious nature … and tendency to corrupt tech it comes in contact with.)