I've done the Brussels_Aachen and Brussels-Paris trips. The drive to Aachen is a pleasant enough one, over decent 2-lane roads. You'll have slow trucks to pass, but much of the route is straight and flat (as you might expect in Belgium) so you'll be able to pass/overtake. You do go through plenty of towns, which both slows down the trip and makes for some pleasant sightseeing. Aachen is a delightful town -- don't pass up the breads from the bakeries there.

The Brussels-Paris trip is on limited-access divided highway (equivalent to US interstate highways), and you'll have plenty of company much of the way, especially between Paris and CDG. The scenery is stupefyingly boring.

Overall, your itinerary sounds like one that I'd avoid like the plague: lots of time in cars, extremely tiring, with little time to enjoy the places you go to.