LOD0 of NuMesis is 56232[parent] + 149278[children] = 205510 tris in total. The polycount doesn't really matter as long as mesh is properly mapped. Nemesis uses 5 unique textures, but it's actually pretty high for UVed mesh. I made shivan corvette of about 70k tris and she still use single texture. You just need enough UV space to keep your maps sharp. Amount of unique materials depends fully on amount of surfaces and size of your ship.
You need to establish a compromise between quality and amount of unique materials your mesh use. Fewer materials [unique texture slots model uses] - the better, but also you risk quality of your texture.
Look at HTL Typhon, for example. It's textures are quite blurry because it uses only single texture slot. GalEmp prefers to UV his ships for maximum efficiency, sacrificing some quality. Scooby Doo's ships are the other end. His ships use many unique UV textures + shared textures of details etc. Scooby's ships looks very sharp and detailed at close distance even with 2048x2048px maps, but also his models are also quite resource consuming. My ships are between Scooby and GalEmp.
Now it's your time. Pick your poison. I picked both + I acquired skills of making "tight-as-****" packed UV maps :]
Also you don't need detailboxes. I like them, but it's not a neccesity. If your mesh is more than 65536 vertices+normals in total, you can just split the middle part and include it in hierarchy as child of LOD0. See HTL Hades for example.
Huh, and LOD1 of Nemesis is 61488, LOD2 is 18346 and LOD3 is 4902