I can recommend a trip on the river, especially if you get an English speaking guide as they can give you a lot of info about the city. It is very beautiful walking along the river to spot the modern statutes too.
There is a tourist bus company which is well worth investing in. They have 3 main routes and these take in virtually all Paris. You buy a daily or weekly ticket and can chop and change between the routes. They are well publicised all over the city. I found it gave me a good basis to make sure I saw everything.
Some of my favourite things to do in Paris:
1. Just go up to Montmartre and sit having a coffee at a pavement café and watching Parisian life go by.
2. There is a beautiful walk down from the Sacré Coeur through the Square D'Anvers which is very beautiful.
3. If you head off into the Latin quarter you will find several jazz clubs and piano bars abound.
4. A walk along the Left Bank looking at the art and books on display on the stalls there. Everytime we go there we manage to pick up something for the house. It is an exciting and vibrant place to be.
I found Parisians very helpful and always willing to help school-girl-french. They seem to love it when you try to speak their language and will spend time teaching you the correct pronunciation etc.
One of the best pieces of advice I can give though is - GET A GOOD GUIDE BOOK!
As to a DMC shop - WHERE? I found a derth of craft shops, although there are quite a few fabric shops around and a whole road of them going up to the Sacré Coeur.