Hi Whirly
Mrs PhilD and I made the trip from Saltzburg to Sourthern England last May, as the return leg of a trip to Prague. It was also the first time that I had been out of the UK/NE France area.
We routed to the north of Munich (more on this below), then more or less on a direct track to Rheims, where we stopped for fuel, then to Le Touquet and back across the channel. The Salzburg-Rheims leg took 3:10 in the Arrow at 140kts, but I assume that either your trusty 150 or you will need to stop before then!
We landed in Germany on the way out (at Frankfurt Hahn) where silencers were not an issue, but I can't comment on silencers at other German airfields.
We intended to stay 1 night in Salzburg, and then stop in France on the way back, but there was a low-level stratus around Salzburg that prevented us getting out, so we had to go back for a day's sightseeing at Salzburg castle, coffee and cream cakes, dinner and a second night in our hotel (shame!). The next day it was slightly better, and the very helpful man in the fantastic weather facility in the amazing GA Terminal at Salzburg found us a route where we could stay VFR. I hadn't done any research on the climate at that time of year, so this may be a problem, but we were only delayed one day.
As far as procedures go, we had absolutely no problems, we just called-up the FIS units as we flew across Germany and France, and they were really helpful, guiding us around the bits of Class D etc. I don't think you need to do much preparation here, just the basic on VFR cruising levels etc.
I used the Jepp maps in Germany and France, mainly as I find them easy to read, and it means you have the same format across both countries. I would certainly use them if I did the same type of trip again. I also bought a Bottlang Trip Kit, so that I had up-to-date airfield charts, and I would certainly recommend that you do this, as it means that you have the airfield plates for any unexpected detours etc.
IMHO Saltzburg is a great GA destination, a good airport quite close to the city, with a fantastic GA terminal and very helpful staff, more like the US than the UK. The city itself has loads to offer, as I'm sure you know.
I'm sure you will have a great time and look forward to the story...