How Strenuous for 1 Driver?
 

Using Brussels as a hub how strenous would the following itinerary be? The mode of transport:driving.

Day1 Brussels-Amsterdam-Brussels(day trip)
Day2 Brussels-Aachen-Brussels(day trip)
Day3 Brussels-Paris( 2 day stay)
Day5 Paris-Hamburg( 3day stay
Day8 Hamburg-Brussels

Thanks in advance!

Quite tiring and useless unless your appointments are outside the cities themselves.

Depending when you are going, you will encounter a lot of fog. Very dangerous.

I would recommend getting a Eurailpass 1st Class and enjoy all the trips. Very good connections everywhere.

If you insist in driving, rent a car with satellite navigation, will be useful to get into the big cities.
Costs are going to be horrendous for parking.
In Paris go first to a Tabac Shop to buy a parking card. Many clocks do not take money anymore.

Have a good trip.

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.

Almost all your trips are covered by the Thalys international high-speed rail network, which is fast, comfortable and reliable. The only exception is Hamburg, which would require you to change in Cologne. I'd recommed this way above driving.

I need to travel by car because there are some smaller places along the way that I might need to visit. Ideally I could just fly from Paris to Hamburg, but I end up renting a car in Hamburg because I have to go to Bremerhaven, Hanover, and a small town 15 minutes south of Hanover.

Brussels-Amsterdam is easy and can certainly be done in a day, same for Brussels Paris, the only long trip will be Paris-Hamburg but depending on traffic you'll be able to speed along nicely on the Autobahn...