The coldest temperature I remember riding in this past winter was -18 fahrenheit. There were many days this winter that it got colder than that, but that was usually earlier in the morning, this is the lowest temperature I remember seeing on the TV news or my phone as I walked out the door (and note this was the actual temperature, NOT the windchill -- those get up to -30s and even -40s here in Wisconsin). I would guess there were at least a dozen or two dozen rides between -18 and 0. We had one particularly soul-draining stretch where the temperature stayed below freezing continuously for 30 days, and a particularly nasty interlude within it that it stayed below zero for about three days straight.
I know most people would not want to keeping biking into these extremes (truly I did not "enjoy" it either -- I just needed to get to work and continue getting exercise). But my general point here is that you can literally ride in any weather. For anyone who wants to extend their season this much, as far as clothing, the important things are the head and extremities, especially hands, nose, and ears. My most carefully selected clothing was my gloves, supplemented by "bar mitts" on the handlebars on the coldest (below zero) days. For helmet get one with insulated ear covering built in & the ability to close vents; these are often market as skiing helmets, but work just as well for biking. Then under the helmet, for any temperatures much below freezing (or higher depending on your tolerance to cold) wear a thin balaclava to protect your nose and face. As far as coat and pants, I don't think it matters that much if you have everything else well covered, or maybe you are going much longer distances than what you said. I actually wore a lighter coat to bike than I did while walking, for better movement, and also the biking generates more heat. Really the most important thing is that it have an insulated high neck and mechanism to tighten around wrists and waist. Most days I just wore my normal work pants; only on the coldest days (well below zero) did I put on snowpants. My single largest expense was the gloves, around $60, and my total biking-specific clothing expenditure was maybe $125 (gloves, bar mitts, balaclava, helmet, and goggles -- see below)
The one thing that applies to the temperatures you are talking about (other than gloves and a normal hat) is IMO you should wear goggles. Even if you wear glasses, like me, there are OTG (over the glass) models you can wear. When looking for them, look for ones marketed for motorcycling. Especially at the sustained speeds you reach on an e-bike, the windchill gets pretty nasty, and even above freezing you can start to feel pain in your eyes from the cold without them. Well, at least I can! With goggles you can introduce a new problem though -- they fog up. But IME, as long as you give the air inside them a chance to acclimate (meaning don't put them on inside, walk out and then put them on) it doesn't become a serious concern until below zero, and/or you are pedaling hard or overdressed (sweating).
