Might as wel react here, been there several times
First, temperatures, it might be freezing cold, even in the valley, or bloody hot, you never know what you gonna get.
Check the French, and other Alpine countrys, wetherpredictions, they're mostly spot on. Or the locals, most of them know how to read the weather better than an email.
Camping in the Alps => Always take warm gear, nothing as bad as staying awake 'cause it's to bloody cold to sleep

A warm sleepingbag (comfourtzone around 0°C), and if needed some thermals.
About the roads, some mountainpasses might be closed, some might be open. There are touristycal one's, and important liaisonroads, no need to explain which one is gonna be reopened the earliest, or stay open the longest.
In Switzerland and Austria you're gonna need a vignet to ride the motorway, then again, why ride the motorway overthere

Avoid the citycenters in Suisse, they're crowded, every 5m there's a red light, and passing through traffic in between cars is not allowed, and the Swiss don't like it when you do it anyway

They'd rather bounce you of the road than let you get thrue

Also, speedcontrols are very strict. I always ride at the maximum given speed limit in villages and so, once outside, the throttle is opened. They might check your speed aswel overthere, but I've heard they concentrate in the villages. This goes for especialy Suisse and Austria, but also a bit for France.
The Belgian ardennes are very nice, but I'd do it in my way towards the mountains, once you've been overthere, al the rest is just disapointing.
So I'd go through the Ardennes (try to ride the valleys of the Maas/Meuse, the Semois and the Lesse) and then go further towards La Roche, Durbuy, and so on to Bastogne, where you easily can get to Luxemburg, where gas is cheap.
Luxemburg city is very nice, if possible, stay there for a night in a hotel, and enjoy a walk in the old citycenter at night.
From there you can get to, and ride the most beautiful roads of the Alzace/Vosges, al in one day. (Ballon d'Alsace, Col de la Shlucht, Col du Platserwassel,...)
Then you're almost, or less than a day's ride away from the Swiss Alps, try to go over the Col de la Vue des Alps if the weather's nice, you'l see more than 75% of the Alps from there, avoid Bern, and head for the Interlaken/Meiringen region, where you have 5 (or 6 when you do the old and the new St. Gothard) of the nicest roads in Switzerland.
From there towards Austria, maybe over Liechtenstein. Stop for gas in Switzerland as it's a lot cheaper than it's surrounding countrys, even than Austria, which is the second cheapest in the Alpine region (exept the Livigno region, but getting there isn't so easy)
Anyway, once in Austria, go down to the Dolomites (mostly better weather than the Northern Alpine side) and ride through the Italian speaking part of Suisse into France, heading down to at least the region around Castellane.
Do the Gorge du Verdon, and head back north using the Route de Grands Alps.
Hmm, long text, isn't it
Anyway, enjoy, if needed, ask more questions
Grtz, Philip!