On Android and I believe IOS it’s a single connection. I would start with the basic functionality (also don’t create a tailscale account with GitHub bc it does weird things with sharing if you ever want to have multiple users).
Once you’ve got the VPN and storage working I can think of two options to give you the functionality of 2 vpns
tasker is an android app that can let you automate a lot. It might let you switch vpns when opening say your storage app and switch back a bit easier than toggling it in settings.
setup your lap-server at home with an outgoing public VPN so traffic goes mobile device> tailscale> public VPN. Essentially acting like you’re home using your public VPN. This may take some tinkering to work properly, especially when you’re home on the same network. Plus you would definitely see a Network speed impact on your phone.