No need to back up the programs, they would have to be reinstalled for them to work on the new computer or on your old computer if you had to replace or format the hard drive.

I use One Drive to backup my files. I get 1 terabyte of storage on each of the computers that I install Office 365 on. Retail that is $100 per year for 10 devices. Microsoft is changing the number of computers that you can install Office 365 on to unlimited next month. It's kind of complicated so look at the link for a better explanation.

https://www.howtogeek.com/364457/why-microsofts-office-365-is-a-great-deal/