If the roof deck is on the warm side of the EPS there is no insulation between the roof deck and the interior conditioned space, the only way to get condensation at the roof deck is if it's cold enough indoors that your breath is condensing on everything else.  You only need to vent a roof deck if it's on the outside (cold side) of the insulation layer.

Ice damming is the result of uneven roof temps, often caused by heat leaks- either air leaks through the insulation layer or less-insulated sections below. Often the thermal short-circuit of the rafters in an unvented roof deck is enough to get it started.  But with multiple layers of EP (seams overlapped), all outside the structural timbers, the only unevenness  temps will be from variable snow depths and wind/sun shadowing, which are far lower factors.  In most of New England an inch of XPS between the shingles & roof deck is often "the cure" for ice damming. YMMV, but if you're using 6-12" of EPS methinks there is zero additional benefit to be had from ventilating the roof deck (and lots of downside from the thermal bypassing of the insulation.)

It's generally better to have the EPDM above the EPS, since meltwater/leakwater that somehow makes it through can otherwise saturate the lower layers of EPS undetected over time, reducing it's insulating value.  With poly above & EPDM below the EPS would not be able to dry- it's a classic vapor trap, even if there's no rot problem with the EPS.  Stone ballasted EPDM over EPS insulation is done all the time in commercial construction, and is directly relevant to your shed roof stackup. While this may violate your sense of the world by putting the highly vapor retardent EPDM on the "wrong" side of the assembly, if all of the wood is on the warm side (which it is), and the insulation is air-impermeable (which sheet EPS is),  placing it on the exterior is not a problem.

It's necessary to apply a slip sheet  between the EPS & EPDM for long term reliability, but it's cheap stuff, available through distributors of EPS & iso roofing insulation. (You might be able to use cheap poly if the roof temps are well-bounded in summer, but the purpose-specific slip papers & laminates will have a higher operating temperature range.)

Inverted roofs (insulation over the membrane) are also frequently used in commercial construction, usually on concrete slabs. It is important to have positive slope on the underlying structure/substructure to prevent ponding, which is what will cause the saturation of insulation over time. Filter fabric should be used instead of poly under the ballast to permit drying.

Properly done, I think either system will serve you well.

Depending on your layup, the EPDM sheet manufacturer may recommend/require attachment to warranty against uplift.

Bruce