I’ve got a jailbroken iphone. I’ve got some apps which i have used and have a lot of notes on, some programs bought on itunes. For example note programs, and i really need to back them up to my pc in case something happens to the iphone. How can i do this?

I recently switched computer and had to authorize another computer for my itunes/iphone account. I noticed that my Iphone apps that I downloaded on the other computer were not present here, how do I transfer it into my now computer? Do I have to rebuy the apps?