The number of indoor cameras required basically depends upon the structure of your property, the size of the area you want to cover, etc. If you think that covering all the rooms and closed spaces is not possible, you can opt to install the camera in the hallway which the intruder will have to walk down in order to reach the different rooms.
The service providers listed at Sulekha are extremely competent. They always provide you with an approximate budget and tell you about the best possible alternatives to cover your space with cameras.