I use medium scale 32" Chromes on my Beatle copy. .100 E string. 30" scale bass. I don't find it too floppy but it is the nature of the beast. LaBella has a set just for the Hofner style basses that a lot of people will endorse.
Back to questions: 1. 33% scale 33% construction 33% string
3. Possibly... I find that the diameter of the string, larger being tighter, smaller softer, is a good rule.