In Frankfurt, for your work trip, will you be at the Messe for a trade show, or will you be in the centre of Frankfurt (a.Main - you do mean Frankfurt am Main, not the one on e eastern border, right?)?
Assuming F a.M can you fly home from Paris or can you fly home from Milano?
It makes little sense to go southeast and south and wind up northwest of your origin.
More sensible is to go to Paris first, which is the real outlier of the bunch, then either fast train or fly to Munich from where Füssen is an easy day trip (although there are many many other real castles much easier on your route, Neuschwanstein is only a late 19th century imagination of what a castle should look like, but if that is the image in your head and that of your wife by all means go), and then you can continue a couple of hours to Salzburg and thence to Hallstatt.
From Hallstatt to one of the villages in the Cinque Terre will be a difficult day's travel because both of the places are remote and difficult to reach. But, it can be done. I'd never do it. I suppose one way would be to return to Salzburg, then train to Innsbruck for the train to Verona, then change for the train to Milano, then change for the train to Genova, then the Regionale train to your destination.
You will be passing some fabulous places - not least Venice (and I never pass up a chance for Venice) - as you go to all your out-of-the-way places.
I don't know if there might be a cheap flight available to pop you over the Alps between Salzburg and Milano to short circuit some of that long long day.
I usually counsel against Eurailpasses because of the outrageous prices plus inconveniences, but for the long journeys you are planning, particularly if you are forced to return all the way to Paris at the end - maybe, just maybe, it may work out for you.
I don't think you have too many places for 14 days, just that you have picked really out of the way places which are a devil to travel between.
