The return lines are self-bleeding when the engine runs. Since they're not on the delivery side of things, they're typically not bled.

Be aware that the M pump you have is slightly different than the MW pumps used on the 617's. You can tweak the fuel a bit without touching the idle adjustment. Typically it is only adjusted when there is an issue with idle quality. The EDS tends to keep the idle adjusted and will override the internal idle adjustments. Typically you adjust the idle controls with the EDS solenoid unplugged and aim for ~500-550RPM in park. Hunting idle or failing to idle after a rev indicates the need to adjust the idle stop.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]