Take your V5 with you, and stop at the first TÜV place you see in Germany. They’ll do you an Umweltplakette there and then. Typically 5-8€, depending on stuff. Dekra do them as well, but they’re 14€ there for some reason. Do your Critair thing now, and print out your receipt. Leave it on the dash if you have to park in a French city.
You can buy a toll tag in some service areas – sometimes from a vending machine, sometimes from the APPR/ARREA kiosk. They are absolutely worth getting, especially the ones that do Italy and Spain as well, as Italian toll areas can be a proper clusterfornication.
You’ll need a vignette for Austria and Switzerland if you plan to go through them. You can do that online these days, which sucks because I like stickers! I avoid Switzerland in its entirety – their vignette is 40€ and even 1kmh over the limit is a fine of about a quarter million francs and it’s easier for me mentally to just not go there.
Priority from the right has been covered, but it’s common in Belgium and NL as well. Less so in Germany.
Use Waze or Flitsmeister – they’re not just for warning you of speed traps, they’re great for hazard notifications as well.
You’ve got a ‘free’ threshold in France as well – 5 or 10% above the autoroute limit is ignored, then 10 to 20% above is 90€, or 45€ if you pay quickly. This is useful because France is huge. I’m on NL plates, though. So I do actually get fined by post. With ‘rosbief’ plates YMMV…