Well firstly the impulse engines are not pointing up, they're angled and are located above and below the secondary hull so in total there are 4 and allows quick manoeuvres. Due to the engines being shaped the way they are they look square when viewed from above.
The saucer is connected to the secondary hull, as I said before, centrally. In a way you could say the edge of the saucer is embedded in the secondary hull, at least that's what it would look like.
As for what are the light blue lines, why they're aesthetic of course.![]()
I'm already doodling my own sketches of it from scratch. I bet I can make your concept look fab. Mind you, it's going to conform to MY design sensibilities, so it will end up looking like the Ent-D did compared to TOS Enterprise...