Never try to keep water out of a building using impermeable coatings, rubberised paint, ciment render, etc etc. A building MUST breath, even at the cost of some inward moisture during wetter periods, any water that will inevitably creap in,and even the moisture you create by living in the building,needs to escape, or I guarantee you will have mould and rot problems down the line. Water which can not escape from behind an impermeable coating is worse that no coating at all. I recommend a lime render for all building needs.
You need to investigate owncloud, it is a self hosted cloud drive, think Dropbox, the pi is the machine in my house which is already internet facing, and has a wordpress blog running, with a domain name attached, so it made sense to use that. The owncloud android app sends all my photos and videos to the pi, and then when I am at my pc, the owncloud windows app pulls the files from the pi,so all files are synced. Once set up correctly, all of this happens without any manual intervention, and files are stored in 3 physical discs, my phone, my pi ext hard drive,and my PC. I also have an off site backup on oracle S3 Archive.
Sounds similar to my needs. My solution was a self hosted instance of own cloud on a raspberry pi 4 (nextcloud was good but too too many bells and whistles, and was unstable on my system). The owncloud android app automatically transfers my photos and videos, which are then automatically downloaded to my main PC. Important: This is not a backup solution, if I delete a photo from one instance, it will be be deleted on all instances. This system had physical redundancy, as all photos are on at least 2 separate devices at a time.