Hi Caz, you're nearly there:
Yes, it's in E minor - the Imaj7 chord is from the parallel key of E major.
Cmaj7 is a bVImaj7
D9 is a bVII9 - it functions as a substitute for the V chord (sometimes referred to as a backdoor dominant)
Fmaj7 is a bIImaj7 and is from the parallel E Phrygian mode
Don't view G as borrowed from the parallel major, it's diatonic to C (harmonic) minor
Maxwell's Silver Hammer is not difficult, it just contains a few secondary dominants (indicated by V7/_ on the chart below):