Darks need the information of the camera as it was during the actual photo shoot. Info like heat and dead pixels.
So you take them at the end of each session with all the settings the same as the actual pictures, ISO, exposure time, Aperture.
Flat frames are used to eliminate vignetting and dust from the stacked light frames. So in your current setup, almost no moving parts, it's cool to take them any time you want and re-use the resulting masterflat from DSS for many months. (For each individual lens a separate masterflat.)
I don't know anything about bias. Never bothered. But that is not a qualified attitude!
I am thoroughly impressed with your cropped Orion photo! Is that a stack of several 3.5 secs exposures or a single frame?
Get that barndoor mount going!
Imagine how much more detail you get to capture and investigate from Orion with several exposures of, say, 15 seconds or more!!