I am a stubborn, non-gearhead biker, so please take any of this with a grain of salt. I biked to work for ~12 years everyday in Tampa, and I bike commute as needed (but work from home) for ~4 years in Nova Scotia.
When I worked in an office, I left outer clothes (work pants, dress shirt, shoes) in my office. That was very handy. On an e-bike, though, that might be less of an issue (as long as the weather is good).
For the rain, if it's warm, I sometimes found it easier to change when I got there than to stay dry. When I lived in Tampa, I would sometimes bike to work in swim shorts and a quick dry t-shirt and change into dry clothes at work (hanging the wet stuff in my office). In the cold, I like a cheap vinyl rainsuit. It stays very dry, but it gets hot (so I don't like it when it's warm). Now that I live in Nova Scotia, I use it more.
I typically carry my stuff in a backpack dropped into a milk crate strapped to the back shelf on my bike. Rather than get a waterproof backpack, I keep a garbage bag in my backpack, and if it's raining I drop my backpack into that before dropping it into the milk crate.
For snow, I haven't done anything special to my tires, but I primarily ride on cleared sidewalks. The salt can be a mess, so I rinse my bike off when I get home with some warm water.
One cool thing that I keep thinking about getting is some waterproof and windproof handlebar mitts. I haven't found any gloves that are warm enough and flexible enough, so this seems like a good solution but I haven't actually done it yet. Something like this:
https://www.amazon.com/ROCK-BROS-Handlebar-Windproof-Coldproof/dp/B07WV274XZ/