Accomodation in Paris

Me and my friend's family are travelling to Paris in July. I need to know the following:
1. Name a few Budget hotels / service apartments (with kitchen) in a safe surrounding
2. Places of interest (for a 3 days trip)
3. Recommended area for stay for a family with kids (close to super markets)
4. Other than Paris any city/ town a must visit?
5. What is the main mode of transport for local sight seeing and how much normally does it cost?

I hope weather will be gud and no rains ?

Are 3- days enough for Paris?

Any advice will be greatly appreciated.

Thanks