I like to prime and paint the entire model, by leaving off roadwheels, track, and turret until all painting, decaling, washing, and drybrushing is completed. As far as the fiddly-bits are concerned (pioneer tools,etc.), I paint them right on the tank, unless they are in hard-to-reach areas like the Tamiya Marder III. In those cases, they are painted off the tank and added later. Likewise, ammo boxes, bedrolls, etc. are painted, washed and drybrushed and added at the end with a little superglue. Everything is then flat coated and assembled. There is, of course, variation depending on the model
Quite honestly, there is no "proper way" to finish a model. What works for us may not be appealing to you, and vice-versa. Take some of the suggestions you see in these threads and try 'em. Discard the ones you don't like or won't work and keep the rest. You're the artist here; create, discover, and have fun!
Gip Winecoff