Linux Mint is a great way to start. Syncthing is a syncing tool that will run on your computer and your phone. It's decentralized and a great way to sync folders between devices. You can even share folder with a friend if they also use syncthing. Proton Drive is a good intermediate step, but syncthing will allow you to be more in control of your data. KeepassXC is a password manager that will also work on your computer and phone. If you pair it with syncthing, then you can synchronize keepassXC between devices, so no need for a cloud service. Tor Browser is useful to keep around for more private web browsing.