I agree that it´s always good to have your bike well serviced before you leave. But I actually worked for Honda spare parts for many years, and I can tell, that the Honda dealer network in Europe is never very far away. The Goldwing is a special bike regarding spares (especially if it´s gone down!)... but all in all, I wouldnt be too worried about getting parts. The availability is as close as it gets to the US I think.

Regards shipping, I´m sure these specialised, readymade packages are the easiest way to go, and surely worth considering, especially for a 1st-timer. But they do cost a bit, too. And lots of stuff, including vehicles, gets shipped across the Atlantic all the time, so you can also do it by yourself (or with the help of a ´normal´ freight agent), too, and save some money in the process. Guaranteed it will be more work that way, you´ll need to pack the bike into a crate, for example (and unpack at the destination), and also you´ll need to make the package as tiny as you can, to get the costs down.

You´re right about the traffic laws, control is getting tighter, and fines are getting higher, especially in Western Europe and Scandinavia. Norway & Switzerland are good examples of countries, where you can get nasty fines. But still there are lots and lots of nice roads in both of them, where you´ll seldom see any cops! Be careful inside the city limits, and on bigger roads with heavy traffic.

GPS - funny I´ve never owned one (or actually I now have it in my phone, but doesnt get used very often).... I once tested a bike in Lake Como, Italy, with a GPS on it, and as that area has a lot of population, lots and lots of tiny roads turning here and there, I must admit, that it really was very useful in that kind of area. Would be the same in more or less every big city, too I think. But on the other hand, I´ve done over 20 mc-trips to Europe without one, and never been really badly lost, you can find really good paper maps, too. So I wouldnt say a GPS is mandatory. If you already got one, then sure bring it over.

All in all, Europe is quite easy to do on a bike, roads are good, and accommodation is easy to find. And you can often get along in English, too. The downside is it´s not cheap, and again the West and Scandinavia are probably the most expensive areas.