Hard to say what is the ‘best’ approach; a lot is preference, but:
always try to model to scale.
In this case I would not model it in one piece. The ‘main body’ looks kinda blocky; maybe use just a Bevel Modifier on a simple shape.
The tower for instance looks like it wants to be made with a Subdivision Surface Modifier.
It is easier to model in different pieces, when you are using different modifiers (otherwise you’d have to ‘separate’ them with vertex groups).
Try not to loose yourself in modeling details that you will never see, (because you are too far away).