That sounds like a good plan to me. Je suis fou de Paris! I have been to Paris six times and spent a total of two and a half months in the city. There is just so much you can do in that city. BUT for a first trip I would suggest you get an apartment. you may save some money over a hotel and you may find it convenient and save some money to cook a couple meals for your self, especially breakfast.
There are may day trips that you can do from Paris, like the Chateau de Versailles, and you do not have change hotels to do these trips. Do a search for "Day trips from Paris" and you will find many to pick from. French_mistique has posted a nice list to possible day trips from Paris.
Here is a lot of information on Paris: http://anyportinastorm.proboards.com/board/46/paris There a many things to do in Paris and this will give you and idea of some of your options. There are many photo essays that you will find of interest to help you decide how to plan your day.
An example of a day trip from Paris that I did a number of years ago was to visit the city of Angers. I took an early TGV train from Montparnass to Angers, about a two hour trip. The Angers train station is will located in the city center so you could walk to the Chateau d'Angers. the old part of the city and some beautiful gardens and take a late train back to Paris. I am sure here could suggest more trips for you.
You might consider getting a Bato Bus ticket for one day and use that instead of the Metro to get you around Paris along the river, they stop at a number of locations and you can get on and off at any of these with that ticket.http://anyportinastorm.proboards.com/board/46/paris
Yes do visit the chateaus in the Loire valley. I have seen a number of them and on the previous web site mentioned above you may find information on may of them in the France section and some may be photo essays. You could rent a car or there are tours available in Paris. I am not a tour bus fan, those bus seats were worse than the air line seats. The D Day beaches might also be a place of interest to you.
I am sure you will really like Paris, but if you don't,just do more day trip from the city. France is a beautiful country and I am sure you will have a wonderful trip. I like your travel style, take some time and enjoy the trip and not trying to cram everything into a couple days.
If you do get an apartment, I am sure you will find shopping in one of the supermarkets and find many new items you have never seen at home. Or going to the local bakery every morning for a fresh baguette. The here are many markets in Paris you may like to visit, check to see where they will be and the days they will be open. I always would try to stop at BHV, the department store near the Hotel de Ville. There is much to see there and I especially like the basement level where they had the French hardware, many things I could never find where I live. You can get house numbers for you home like the ones in Paris and many other things of interest.