Maximum amount of LOD models

[thebigroyboyski]

I was just wondering if there is a maximum amount of LOD models you can use and if you use too many can it have a negative effect with the amount of models being loaded.
For my latest model I want it highly detailed close up but as it's a wagon it needs to perform when there is 100 of them. I know textures will also have a big effect on this too.
Also when i'm building the lower poly models do I build as a seperate new mesh or do i just stack them all up in one mesh?
I'm using Blender now so i can hide parts and build on the same coordinates.
With my Frontrunner I only used LODs to make small parts disappear so i'm new to using multiple meshes.

Cheers
Roy