fastest way to efficiently restore a poorly maintained system (data is not needed but needed to be archived)

when i visit a friend on Monday, i was requested to restore his pc and phone since it is overloaded and he has never done maintenance and little naive on how to do it and also
has a busy schedule and not giving this a priority..

i will have a whole day with him.. while the family has the picnic going on, i thought i will help him.

what would you suggest as a the rapidfire/quick way to do a complete restore:

the idea i was thinking was this.. since this is coming in very few days, and not much planned yet..
so just a cloud storage.. maybe 1 TB..

do a backup of every user file in his PC and also phone. (this may take hours, but he has cable internet so could speed up)..

he does not want regular access to his files, but would like an archive of them. (including photos and other media files)

after the backup is complete (on cloud)

then i can do a complete factory default on the smartphone
and also reinstall from scratch on the PC..

then he feels ok to go to cloud as needed to access only files that will be needed for the next week..

can you comment on my plan in the mind.. how would suggest differently or to make this process more efficient, given have only 2-3 days to be onsite and get the job done before sunset! (when we will drive back)

thanks~