When is your trip?
If your flights are fixed, and you only have 5 nights, and you want to rent a car, those parameters will significantly shape/limit/focus your itinerary. That's not a criticism, just a fact. Some more points to consider as you make your itinerary:
- Two nights in a place equals one full day. One night in a place means less than a full day.
- The day of arrival is often a jet lagged haze, and the last day is taken up with getting to the airport for your departure (unless you have a VERY late departure, in which case you can genuinely have a half day of sightseeing). So, if you have 5 nights, you only have 5 days, and the first day you shouldn't plan anything too strenuous. Jet lag hits everyone differently (I find it's different on every trip); don't plan too much on the arrival day.
- It takes at least a half day to change places - checking out, getting from one place to another (including the inevitable time spent finding your way out of town in the beginning and finding the location of your new hotel at the end), and checking in. I had read and repeated this for years, but having just taken a driving trip in Sicily, it really took on new meaning. Even places that were only two hours apart on a highway took longer than that to reach door-to-door, because once you're off the highway and on surface roads, things get harder and slower (yes, even with a GPS). So, we really lost a half day with driving between destinations.
- With only 5 nights to play with, I'd have overnight stays in one or two different places, tops.
- Cities like Paris and Brussels are best connected by train, not car. If you are going to drive into a city, allow €20-25 per day for parking, not to mention lots of time for traffic. Or, stay out of cities and focus on rural areas and smaller towns. Or, give up on the car and take trains instead. You can always stay in a smaller city (like Bruges), use the car to see the countryside, and take the train if you want to see cities (like Antwerp, Brussels, or Ghent). In fact, if I were flying in and out of Brussels and only had 5 days, that's probably what I'd do - focus on Belgium. I know you want to see more, but you just don't have time.
- Driving in Switzerland may indeed be very scenic, but in your short time, it's quite far to go from Brussels, unless you make that the whole trip (which of course you could do, if you want). To estimate driving times and costs, use http://viamichelin.com (note that they key word is "estimate").
- Don't look at a guided tour (Rick Steves or anyone else's) and assume you can duplicate this pace. On a tour, someone else is taking care of logistics and knows where they're going, so they can go faster than an independent traveler can.
Again, I see that this sounds harsh, but it is just the reality of travel. We all have to make these difficult decisions on what to see and what to omit, how to get around, etc. Ultimately, less is more; if you try to see "everything," you will end up not remembering anything but the inside of your car.
You should get some guidebooks on France and Belgium, figure out what interests you, then base your plans on that.