Take one carry-on suitcase and a shoulder bag. Wear a raincoat. Get a pocketful of 10-franc pieces to pay for ground transportation and you'll stay ahead of the crowds. Feed Tizzy right away. She'll be broke.
Sightseeing is nice, but exploring is better.
Having now done the big five on foot, I'd put Notre Dame, the Eiffel Tower and the Arc de Triomphe in the drive-by category. The first two are tourist hells. The Arc is in the middle of a busy traffic circle. The upper Champs Elysees has become an Americanized mall where you will find teenies from every corner of the world inhaling French fries from what they call MacDo's. Straight to the heart Head down the Champs as fast as you can until you hit the Tuileries, then cut to the left past the Elysee Palace and turn right on Rue St. Honore toward the Madeleine cathedral.