The name of a roof section between converging valleys

"What is considered an acceptable angle for a roof to ensure that there will be sufficient run-off during rain conditions?"

Generally, minimum slope for water to run off is 1% (1/8" per 1'). However, minimum slope for a flat roof by building code here is 2%. (1/4" per 1').

You have more than enough slope for your roof, however you will likely need some sort of membrane roofing since it is very low slope.

There are profiled metal roof cladding systems specifically designed for low-slope application. I don't know if any would be good for a slope as low as what you've got, so that is something you would have to look in to. Maybe call local roofing supplier and see if they have anything that would work for you.

The lowest slope you can do for a shingled roof (that I know of) is 1 in 4.

You mean you have heating coils further up the roof - toward the peak - from the metal? That's not a good idea, since it melts the snow from the bottom up, and the water from that melting runs down onto the metal & freezes there (that's the coldest part of your roof, because the overhang isn't heated by the house's interior). The result is ice damming.

It's also not a very good idea to add heating coils on top of the metal. If for some reason they happen to not function (say a power outage or a switch failure), they'll get torn off by the sliding snow/ice. A better idea is to heat from inside the soffit, allowing that heat to rise through the metal roof.

If that's aluminum, you really should coat it with something; aluminum is hydrophilic, meaning water likes to cling to it either as water or as ice. I'd love to see you replace it with copper, which isn't nearly so hydrophilic.