otherwise 'fit to page' overrides any attempt at scaling.
Fit to Page will fit the drawing to the available paper space without regard to any scale. If you want the drawing set to a scale then you must set the scale.
the simple line drawing tool acquired an enormous arrow.
You must have set it in the "Pen Properties" tool. See screenshot 1.
There seems too be no option with these to prevent the marker lines running to the edge of the workspace
I think you are referring to construction lines. Yes, they are infinite. They can be hidden by hiding the Construction layer or removed by right-clicking an empty space and use the construction line menu option to delete all.
When you first load your drawing if all the dimensions are way too large then select all (cmd-A) and select your custom standard to clean it all up.