Photo editing workflow

The "Save As" dialog contains a slider where you can adjust the level of compression, which is directly related to the file size (and the quality of the final save of course). There is also an Options button in that dialog, which let us adjust even more settings before saving:
prnt.sc/dyuQwYUOLefu

Regarding the workflow steps, they depend of course on the desired outcome. I mean there may be more or less post processing steps for any given image.

I would just like to point out that the 3 post-processing steps you mention also come as adjustment layers. Instead of duplicating the layer in every step, you can simply add the desired adjustment layer on top of the original image. This could also reduce the size of the saved .pspimage file, but more importantly it allows you to adjust your settings even at a later time. This kind of workflow is called non-destructive. Duplicating layers and post processing the original image from the Adjust menu is a destructive workflow, because it applies your adjustments permanently every time.

You can add adjustment layers either from the main menu: Layers -> New Adjustment Layer, or from the bottom part of the layers palette:
prnt.sc/aw06p3Vogalv