Set the origin (Place A) as "current location" and the destination (Place B) as your desired address. Then save that link.
For example:
A current location
B Sydney Opera House, Sydney Opera House, Bennelong Point, Sydney NSW 2000, Australia
The URL will look something like https://www.google.com/maps/dir/-33.8592754,151.2096187/Sydney+Opera+House,+Sydney+Opera+House,+Bennelong+Point,+Sydney+NSW+2000,+Australia/@-33.8592754,151.2096187,9z (there may be more characters, but it will start similarly).
Then change the URL to something else like this:
https://www.google.com/maps/dir/current+location/Sydney+Opera+House,+Sydney+Opera+House,+Bennelong+Point,+Sydney+NSW+2000,+Australia/
So you'll replace the first set of numbers seen (longitude and latitude) with the string current+location and copy all from https to just before @.
Whenever someone clicks on that link it will start from where they are located, no matter where that is, and show directions to your designated location.
Best Answer
So that is the maximum number of tracks that can be contained in one custom map. The actual maximum number could be lower since picture markers are imported into their own layer.
One small thing that might help, if you export a 'directions' layer, as KML (or the whole map), can then import that KML back into a new layer. On reimport it becomes layer of raw 'features' (lines and placemerks) rather than a 'special' layer.
So you can drag the features from this imported layer, into a standard layer. Including many lines in one layer. Bit by bit can then 'move' all the lines to a standard layer. Can then put LOTS (2000) such lines into a single primiatve layer.