Roadtripping from Belgium to Croatia - where to overnight?

In a few weeks time myself and a few of my friends will be driving from Brussels to Petrcane in Croatia.

To plan the route, we've been using Google Maps. First of all, from other people's experience, is it very accurate regarding estimated times of journeys? I'll also be packing my monster sized AA road map of Europe, have always wanted to put it to practice.

We plan on leaving on Wednesday morning to arrive in Petrcane sometime Friday afternoon.

Google claims the journey of 1,604 km will take about 15 hours 20 mins - does that sound about right?

Next question: we plan on ovenighting on two places on the way down: Munich the first night and Ljubljana the second. Does anyone have any better recommendations for places on the route?

We'll be making the return journey a about 10 days later, and would like to take in Venice on the way back. Unfortunately the ferry times from Zadar to Ancona don't really suit us, so it'll have to be overland all the way back up to Brussels. And according to Google maps, we'd be looking at going via Switzerland and Alsace to get back to Brussels on the return leg.

Anyone have any recommendations for must-see sites or cool places to stay on the return leg? Again, for the return leg we have two overnight stops to play around with - though we were thinking of doing the journey with just one overnight, in Como town beside Lake Como.

Here's the route Google suggested for going back to Brussels via Venice.

Also, what are the roads in Croatia like?