Length is dependant on the Train module, for the most part, I would aim to keep these below 30ft / 9m.
I prefer L shapes over a straight layout if I have the room as it allows people to move around a layout.
With no stanchions allow a set back of 6″ from the fence to the edge of the table as children and adults will push up and lean on the table as they move around.
Typically requires a Train module like my Lego GBC EV3 Truck but I have seen some nifty very long ramps used as well.
I’ve used this layout in ILUGNY shows.