Toggle hidden files: Ctrl + H
What do you mean by the path of the mounted partition? It's mount point or it's device name ie /dev/sdb?
You can go to / either via the path bar or selecting Other Locations
By can't use caja what do you mean?
Why would you need to set a file manager as a default?
I doubt x-apps will ever make their way into the repository but you're welcome to request them: https://solus-project.com/articles/pack ... ackage/en/