From Garmisch to Fussen

Will you have a rental car? Or do you need public transportation?

There is a bus that goes from Garmisch-Partenkirchen to Füssen by way of Oberammergau. It takes about 2 hrs.

Here is the schedule. Note that, if you want to see the castles, the bus gets to Hohenschwangau about 9 minutes before it gets to Füssen.

Although it takes longer than the direct bus from GaP to Füssen, there are also other options. You can go by train to Reutte in Tirol and from there by bus to Füssen, or you can go by train to Pfronten and from there by bus to Füssen. However, the RVO bus #9606 is probably the best way to Füssen.

Many of the 9606 buses stop at Wieskirche, but only to take on/off passengers, not for a tour.

If it's from the Edelweiss lodge, isn't that restricted to the military?

The RVO bus leaves from the Garmisch-Partenkirchen Bahnhof and stops briefly at Oberammergau, and most buses also stop at Wieskirche before going to Hohenschwangau. The bus costs €8,50 for an all day unlimited bus ride pass. The return bus also stops at Oberammergau; if you pay attention to the schedule, you might get a little bit of sightseeing in O'gau before going on to GaP on the next bus.

Entrance to Neuschwanstein, which includes a guided tour in English, costs €9,00.

So, you can do the entire trip, any day, for €17,50 (about $23).