For your storage question, it's fully explained in the doc: https://docs.xcp-ng.org/storage/#-how-to-modify-an-existing-sr-connection
And yes, it's planned to get the complete error visible in XO, sadly, it's not "obvious" since the error message isn't returned by XAPI when you try to start but by another method we need to call after it fails ("assert can be started here" from the top of my head).
Let me ping @julienXOvates