Depends on what you mean with without slowing down.

Every extra object causes slowdown of course.

5 at ones, I'd say they can even have up to 3.000 or 4.000 polys if they shall be detailed. Skin size 512x512 should be enough, for a FPS where it has to be good from really close distance maybe even 1024x1024.

And very imporant if they are the basis of the game, make LOD models with less polys and smaller textures.