Does Unity have a polygon count limit it can work decently with? Or does it only depend on your machine?
My PC runs Crysis on very high. Does that mean it could handle 5000 poly character models in a Unity game?
Apart from Unity the following poly count budgets are currently the standard in high end games:
Main character: 10,000 to look perfect from near, including complext normal maps, high res textures and other shaders. For some games these go up to 25,000 if detail is most important Enemies: 7,000: you need more of them, including Level Of Detail (LOD), e.g. one of 3,000 for middle distance and 1000 for far distance
Animation: 80 bones is quite usual to animate for instance fingers and face as well
But keep in mind that it becomes more important to think about lightning, shaders, normal maps etc, so a character with 7,000 may look much better than 10,000 with these things.
Yes, it depends on your machine. If it can run Crysis that fast, it's not going to have any problems with only 5000 polys for character models.
I've found that polygon/vertex count is less important than the number of draw calls.
My Radeon HD (forget exact model number) that I bought last March can handle about 1,000 draw calls before my framerate suffers noticeably.
What I've found to be even more important, though, is writing tight script code.
As already stated polygon/vertex count depends on the organization/structuring of the mesh.
I get best results with avoiding uv seams and combining materials.
Sometimes also Mesh.CombineMeshes helps.