Why do you need turbolifts? I assumed that the Oberth-class had point-to-point transporters to ferry crew as needed from the dish to the secondary hull.
Because of everything
Christopher argues
here.

In essence: it's overcomplicated and stupid to build a system that replaces a simpler piece of proven technology with fancier technology just because it's new and "cool." That's not to say that site-to-site transport wouldn't have a place on a starship, but to totally scrap turbolifts--even as backup systems--would be insane. Even buildings that have elevators and escalators install stairs!
Is that a secondary bridge on the back, or just a sensor dome or something?
I don't think it's big enough to be a bridge--in truth, it's there because the painting has a domelike structure there. I figure it may be a sensor or an obervation dome, like the big glowing dome on the classic Enterprise above the shuttle bay doors.
what program are you using.
LightWave 3D.
Thank you.
Long answer or short answer?

It boils down to laying out basic shapes that roughly match the proportions of what I want the final object to look like, then pushing, pulling, and adding and/or deleting points and edges until it has enough detail. Though it was written for a different software package,
this tutorial gives a basic rundown of some elemental techniques for 3D modeling.
So it looks like I was somewhat mistaken about my prior post being the last update. A few friends and I held palaver today about the saucer issue, and my works-for-a-game-studio-and-I'm-really-jealous friend nabbed a copy of the mesh and mocked up a different take, which after some refinement is:

click to enlarge

click to enlarge

click to enlarge
So...yay? Nay? I think it has promise, though I'm still not sold on the ridge running around the middle of the saucer...