I do that trip regularly.
The route Calais - Lille - Mons - Namur (turn right, watch the junction it is fairly sharp) - Luxembourg - top off the fuel tank - Metz - Strasbourg is nearly free of tolls, the road surface varies from awful to just relaid (usually several construction areas where they are ripping out the old surface and relaying it - expect delays) , there are service areas and small parking areas fairly evenly spaced, the speed in Belgium is 120 kph (unless you have a Luxembourg registered car which is apparently exempt) and you get to drive with Belgian drivers. Because it is in Belgium you can stop at a Quick burger and get one of their different and unusual and tasty burgers - not on the highway, your gps should be able to find them just off the road. There is ALWAYS a delay between Luxembourg and Metz.
The route Calais autoroute de péage via St Quentin, Reims, (careful as the autoroute you were on goes away and after a short toll-free bit you are back on another), past Metz and around the corner down to Strasbourg is easy, expensive, usually free flowing, I just sit back and put the cruise control on and let the car take me. It is more km, the speed limit os 130 kph, there are frequent nice Aires and frequent simple ones, fewer truck because the tolls are high, but many fewer exits so you tend not to wander off into the countryside. No Quicks. Most of the major towns have Flunch outlets for inexpensive nutritious food, but on the outskirts of town and not always convenient to rejoin the autoroute. Fuel on the autoroute is expensive, and detouring to Luxembourg for the really cheap stuff is too far out of the way.
Sometimes I go one way, sometimes another.
You ask about waypoints. Will you have come off a trans-channel ferry or tunnel? If so I tend to take the night in Lille or Calais, sometimes Reims or nearby. If going through Belgium I often stop in Luxembourg. If you are actually starting from Calais fresh most people probably go straight through with a lunch break.
