The limit is 65,536 vertices per file part so split any larger meshes into smaller chunks. Also, Rhino command ReduceMesh does a really good job in reducing size while keeping the shape acceptable so optimise the meshes before you internalise or import them to Grasshopper.
You might consider using the SDDisplayExternalGeometry for static meshes to speed up your model, more here.
This tutorial shows you clever ways how to manage data structure in order to keep your models within the limits.
