I think it is a good setup and good motivation as well! Where do you save blockchain data? Do you have an option to mount an external drive on Umbrel with the click of a button? In my case I use docker-compose (custom setup) and mount the external drive at boot as specified in /etc/fstab. If Umbrel doesn't provide an equivalent setting, you could ask for a feature request. The advantage of doing it externally is you could buy separately a NAS to save all that data (let us say it includes family photos), so that you can have an automatic backup in case of disk failure. If you do it for the whole disk on your computer you would probably save uneeded data (related to your OS).