Maximum acceptable shutter count on a used body?

[KmH]

When I retired, again, in 2010, the D300s I had became my primary camera.
I also use a D200 and a D50.

When I am shooting video with the D300s on a tripod I often use the D200 to make stills.
I use the D50 for astrophotography because it has a CCD image sensor, not a CMOS image sensor.