I had "Marlboro" pants just like yours. Got them same way. Wore them to work in a rainstorm. I get to work and notice my crotch feels funny (funnier than usual). I get inside and shinny out of the pants to find the seams are not waterproof and I have a big, wet, upside-down "U" in my pants. Of course I got the usual comments from co-workers. Worst part was the moist 'junk'.
I wear a snowmobile overall for the cold. Zips up both legs, and up the body in front, so it's easy to get on/off--which for me is a big deal. I don't want to spend five minutes dressing or getting undressed every time I ride. It's an HJC. It was about 80 bucks when I bought it, about 5 years ago.
For rain I've got a spiffy rain-suit that's of no particular note. It works. But it should. It was over 200 bucks (Harley acquisition). If I were replacing it, I'd try FrogTogs. They're about 50 bucks for a suit, and the reports I've read are they work well.
I use a turtle-neck sort-of-thing to keep my neck warm. Also, install the Shoei's 'apron' for my chin, when it gets cold.
Heated gloves. I tie-wrap the wires to the clip-ons and plug/un-plug the gloves from them. When not in use, I tuck the wires out of the way. The main line with the switch plugs into my BatteryTender line. During the summer the wires come off.
Feet don't get cold. Heavy wool socks and boots.
I typically ride 20 miles one-way in an average of 25 to 30* F. With the overalls, a hoody, and my leather jacket, and regular pants, that's about my limit.