Help with Munich Itinerary

Like elsewhere in Europe, driving in Germany is not difficult (driving in the center of a large city is usually not fun, though). However, as a general rule, if you pick up a rental car in one country and drop it off in another, you will usually have to pay a large fee for that privilege. Exactly how large that fee is, you need to check with the rental company (typically a few hundred Euro, but may vary significantly).

A car can be handy for Neuschwanstein, but Dachau is easy to access by public transit (details described in Rick's Germany books). Hard to say without knowing more details of your plan (what exactly are your intentions for "the Belgium area"?), but other than Neuschwanstein, I'd be inclined to do most of this region by rail.

I took the train from Venice to Munich which was enjoyable but it is an all day trip. From Florence it would be another hour or two. Since this is your first trip,
i would fly ( and I did on my first trip ).

How many days do you have to go from Munich to Belgium? 5 days in Munich is more than I have ever spent there. It just depends on your interests.

I would spend some time in the middle Rhine - between Mainz and Koblenz.

For a first time visitor, train travel will take you everywhere you want to go unless you need to go to some obscure village that your ancestors came from.

You don't need a car in Munich, probably not great in a city anyway. We took a bus tour to King Lugwig castles, check Viator as they have lots of tours. We stayed at Flemings Hotel by the train station, excellent breakfast, metro easy to use. If you want to drive on to Belgium, pick up a rental at the train station. Munich is very walkable, good museums, Nymphemburg Palace is wonderful and a short tram ride. Visit the beer halls, we took an evening beer tour which was great and I don't drink beer! The Viktualienmarkt is a must as large market in a square. Nice stores in the pedestrian Walking area. I would drive from Munich to Belgium, with stops along the way, the autobahn is easy to drive but if you get in the fast lane, cars will pull up right behind you with flashers on which means you are going too slow! Have a great time.

When you say you have 5 nights scheduled, do you mean you have a hotel booked already? Would you consider breaking up those 5 nights and use some to get to Munich? For example, the Verona - Munich train route. I have done this numerous times. The train goes through the Dolomites through Bolzano and the Brenner pass onto Innsbruck, then Garmisch-Partenkirchen. Check out a route from Florence on Rome2Rio. You might enjoy a stopover in the Alps. I always do.

A typical day trip recommendation for Munich is Salzburg. Innsbruck, Salzburg, Munich make a bit of a triangle via train routes. That is another option to consider. Have fun working it out. Mayself, I always try to include some mountains in my travel, if possible.