We have two cats from the same litter. We use an automated cat feeder that pours enough for each of them (same bowl) 4 times a day. They’re pretty good about portioning and making sure they’re able to eat together. They hardly ever throw up (1-2 times a year). They don’t act hungry, but they do rush from anywhere in the house when they hear the food dispensing. Each cat weighs 13 lbs.
Why write off iCloud? Just turn on the advanced data protection feature for end to end encryption.
If you want to self host, while I’m not familiar with Goodnotes I bet you could write a simple Apple shortcut to take those files to a storage provider like nextcloud then just automate that shortcut to run daily, weekly, whatever.