What you describe is a piece of functionality that we are aware is needed, but unfortunately still not available.
We know that reference lines for general visualizations (not only timeseries visualizations) are needed, and we are planning to add that. It is being scheduled for development in a prioritization process that also includes all other things we want to add in the product.
As soon as Reference Lines are available for the regular Bar Graph, your needs specified as point 2 and 3 will be covered as part of it, since this is already supported by the Bar Graph.
Best regards, Theo Klemming