I know it sounds like basic question, but what exacly dose count as one object? dose windows count as one? what about books in bookshelf? ect...
That is actually up to you. As a rule, you keep it the same as in the real world. So the window frame could be an object, the pane, the handle, etc. But it always depends on the situation, if your window or your bookshelf is only far in the background then the whole window can also be an object. You can also add individual objects to a collection.
According to Blender logic, everything is an object that is displayed here in the outliner
Yeah don't worry, the rules are not set in stone. You can model enough objects that the room feels busy. Try having everyday items where it makes sense. A glass of water on top of the desk, hangers if your closet is open, speakers if you have a computer visible, wall sockets, light switches, cords, etc, etc.