Creating openings before or after subdivision?

Hi everyone,

I am modeling a fuselage of a small civilian propeller plane and I'm having difficulties dealing with cutting out the windows.

I'm modeling as much as I can using subdivisions (Hpyernurbs as its called in my app). I'm also attempting to keep everything in quads, which has been recommended as the ideal way to go.

With my approach to the windows, I projected some splines to use as trace objects for the knife tool to cut out the profile of the window and pilot/co-pilot door from the low poly fuselage. As I've been doing this, I'm running into shading and edge termination issues. The subdivided topology is also difficult to work with.

I'm wondering, would I be better off cutting out windows and other openings after the model has been subdivided or should I try to wing it with a low poly model to SubD? I retained a copy of the original fuselage without the door and window cuts just incase.

I would imagine that the problem is much with the same with other vehicle types. How would you approach subD cuts of a similar nature?

I have attached screenshots of the low poly model with wireframe; subdivided model with wireframe, subdivided model without wireframe and the actual subdivided model in its non-parametric form.

Thanks.