Travel from Fussen to Meersburg

Hi again. The German Railways site gives you the fastest connections by public transport between any two towns of your choosing. This trip you mention will take a little over 4 hours.

https://reiseauskunft.bahn.de//bin/query.exe/en

You can look into all driving times and distances at this page:

https://www.viamichelin.com/web/Routes

That really is out of the way I guess for the places I'm looking at visiting

You're still planning to do the Romantic Road, right? For additional destinations, rather than the detour to Meersburg, maybe see some lovely places near (but not on) the Romantic Road... have a look at the following...

Possible day trips by train from Würzburg (all are within 20-60 minutes of W'burg):
Bamberg
Iphofen
Ochsenfurt
Marktbreit
Bad Windsheim

Okay thanks. I was really interested in seeing Mainau Island but maybe I'll have to skip that part

Mainau Island is on the opposite side of Lake Constance from Meersburg (although you probably could take a ferry)

Getting from Meersburg to Mainau Island is easy. You can either take a direct ship (on the Bregenz - Konstanz route)
https://www.bsb.de/de/fahrplan-online.html or a car ferry from Meersburg to Konstanz-Staad and from there a bus to Mainau. The car ferry is for pedestrians as well and it sails every few minutes.

Okay thanks for all the information. I may be rethinking my whole original plan now