Marche aux puces at Porte de Clignancourt ; is The most important New merchandise  and antiques Flea market in Paris  .
 It is situated at "porte de  Clignancourt " Metro station, and is open weekends . 
Just be careful market is situated in not very safe area , so is not advice able to walk  at night in surrounding streets !

Cafes in paris ;

There are some famous cafes in Paris , and they are part of the city's history, for example cafe de la Paix  at place de L'Opera ,  cafe du Magot and 
cafe de Flore situated at Saint-Germain-des-Prés, etc . These famous cafes are over represented in tourist guides and on the net .

Should not  forget that Paris has some cosmopolitan, friendly and affordable world class Coffee shops also, which are accessible for everyone and will offer you a pleasant drink  and some minutes of relax in quite familiar atmosphere . 
These are Starbucks Cafe , MC Cafe , Columbus Cafe ... and you find them easily in every major streets of Paris like any other Big cities !

paris safety :

Yes , Paris generally speaking is a safe city , particularly  upper class neighborhoods ,  
 around historic  sites and  center of city.
These arrondissements ( city districts ); 1,2,3,4,5,6,7,8,16, south part of 17 . are perfectly
 fine and safe day and night.
These arrondissements : 20,19, 18, 9 , 10, some areas are not recommended to walk at late 
night .There are  still few tourist attractions in these arrondissements like Montmartre , Moulin rouge , 
Flea market of antiques ...
Avoid around the train stations like Gare de nord , Gare de l'est , Gare de Lyon

Very often in the paris Airport terminals or railway stations,  some drivers approach travellers and offer a ride cheaper than taxi, which is not true and depending to the company, their service usually cost much more expensive than Taxi. They have no taximeter and they make their own fare price ! For tourists is not easy to compare quickly those limousine prices with taxi fares, so they often take advantage of uninformed visitors. 

These  are often just the private cars, they don't have taxi sign & logo, neither the registration number, and sometimes they are illegal workers.

According to France Laws, approaching the travellers in Airport terminal, railway stations or any other public places and offering them a ride is illegal and people doing this can be prosecuted.

Remember; Official TAXIS  never  approach travellers to offer their service in Train stations or Airports etc !

If you have no previous booking; Always take un official taxi, which has the  taxi sign  on top of the car roof and has a taximeter on the front dashboard, visible to passengers. 

If you are looking for decent and cheap hotels in paris , there are some solutions ;

IBIS HOTEL  or their economy version ;  IBIS  BUDGET  HOTEL is finest cheap hotels in paris, which  offers the standard, new , clean and basic rooms.  it has very attractive prices; about 60 euros per night.  they have many locations in city of paris and nearby suburbs.  Try to choose a hotel not far from a metro station , that will make  difference in your everyday commute.

So having an inexpensive and decent  hotels in paris is possible, and you can check the website of these hotels, to see their geographic locations and get more informations:  IBIS BUDGET HOTEL .
Or see the website of  IBIS HOTEL. 

Every District of paris has one or Few Pharmacies  staying open late night or even 24 hours. 
By clicking here you see the list of these available pharmacies .

In paris and almost all cities in France shops are traditionally closed sundays, in exception of few holidays per year.
Considering the fact that paris is very important touristic city, government has allowed few centers to stay open for tourists  shopping .
Followings are the shopping centers , districts and streets ,  staying open Sundays:

Ave  Champs  Elysee : Many famous stores located in this Ave will stay open sunday , as :
Louis Vuitton ,  Zara , Virgin megastore , Disney store , Gap , Sephora , Marionnaud  ...

 
Carrousel du Louvre : which is a nice and modern shopping center situated under the glass Pyramid of Louvre museum.

 "Quatre Temps " shopping center in La Defense : 
Is a very big shopping Mall with all king goods and stores situated in "La Defense" District  .
Metro line 1  and  RER line A  , at  Quatre Temps Station .

Le Marais :  Is an old and eccentric  Parisian neighborhood with  fashion designers 
 boutiques of clothes , perfumes , decorations , jewelry  , etc 
Metro Stations : St Paul  Station or Rambuteau  Station .

If you have at least 3-4 hours free time , you can take Taxi to paris .Don't waste time with RER (train) or bus etc . Make sure leave your heavy luggages in concierge and calculate the « real » free time you have before being back in airport . 

You can visit famous monuments and walk in touristic center of Paris or even take double -decker bus tour etc , number of places you can go depends how much time you have .  
At night or very late night you will Find famous Cabarets , nightclubs and international bars , cafes and restaurants , you can find them all in Google . Specially in summer time you will see crowd out up to very late. 
You can Catch a Taxi at any time in front of those places  to CDG. 
Taxi ride from center of Paris to CDG at late night or early morning will be about 35 minutes and in normal day time about 4-50 minutes ( still check the traffic condition and rush hour commute time ). 

CDG customs  & Luggage :

Actually there is  no one  answer to this question ; 

It depends to time of the year or even day of week or hour of day , and also the fact that your arrival coincides with French holidays or not ! 
Usually in normal condition in 30-45 minutes you will be able to pass customs and recuperate your luggages as well.

First of all paris weather is very moderate and it doesn't get very hot in summer ( average 26 ° celsius = 78 Fahrenheit  ) and very seldom it may get few days freezing temperature during winter.

Tourists they come to Paris all year long .

But , is good to know that great number of parisians traditionally leave the town during the month of August for summer vacation !

Paris becomes empty during this month , and is quite strange ; Metros are empty , no traffic in streets etc. 

you can even easily find parking place in the street for your car , which is very difficult task in normal time.

So city will be left to tourists !