For the sake of doing a restoration I just serviced a rear wheel: new bearings, new grease, new axle and new dust caps.
I think I have put enough grease. When spinning the wheel before putting it on the bike I was feeling a bit of crunchiness but no noise. After putting the wheel on, truing it, setting the brakes, I did a spin test: there is no resistance, the wheel does spin for a while with a single push. Unfortunately there is a significant metal on metal noise, feels like a bearing on bearing friction. The wheel has also a tiny bit of play but it is attached safety to the bike.
Here is a video with audio: https://i.stack.imgur.com/9ky3s.jpg
Also, I had to replace the dust caps by a wee bit smaller ones (25mm vs 28mm), but I do not think this is to blame.