ca. 474m (Saucer and nacelle size of the 3D model matched to that of the Galaxy Class from my shop with the same scale. I know most sources say something arround 440m, but it would look odd next to the Galaxy Class if the saucer is smaller.)
Print orientation for Detail Plastic:
Flat, upside up
Hollow, 2mm wall thickness, two aditional holes hidden left and right between the saucer and the engineering hull.
The Nebula Class with the triangular pod. This seemes to be the most common version of this ship.
If you need this in another material, size, quantity or combined with one or more of my other parts for cheaper printing, just let me know. I will try to make it as you need.
If you want to see my custom-made Star Trek Tactics ships, visit my thread on hcrealms.com.