Plotly Express hover options
1 and 2 are not possible yet.
For 3 there is a hovermode attribute in layout that you can set to show one hover label per trace per y-value.
In plotly_express.line the only options I see to modify hover settings are hover_name and hover_data. A few issues I'm facing with modifying hover are:

It seems that even if I set hover_data=None it still shows the values for name,x, and y. How can I set it to only show the hover info I select without adding defaults?
I can't find a setting to modify the opacity for hover boxes. I'm displaying a lot of hover info so my hover box is large, which makes it difficult to know where I am on the plot behind the box.
How can I make it so hovering on one line displays hover info corresponding to a linked data column value on all other lines?