Good to see a fellow TA fan
Sometimes it's good to see a big gear mechanism on the outside. A bit of steampunk can go a long way to making a structure both scifi and believable.
From memory, the spheres on the star destroyers were actually the shield generators, though I may be wrong.
I wouldn't be too concerned about polies. You can do a
lot with 4k polies. Don't forget that you only really need 8 sides to get a near-flawless cylinder/rounded area because of the engine shading. (I use 12 for larger cylinders, and maybe more if it is a very large and very obvious rounded section, but generally not many are needed).