For cold weather riding, I can't say enough good things about wearing wool as the first layer, next to your skin. I wear a wool undershirt, and for everything else regular street clothes. When it's cooler out (35F to 55F), I wear wool socks, and wool gloves. When it's very cold (far below freezing) I have wool knee-warmers and a jacket or sweater. Wearing wool so vastly changed the comfort-level for me when I started doing it that I haven't used anything else since.
Also, do you have a basket or rack on your bike? If so, you might try stowing your jacket on the bike somewhere out-of-the-way while you are riding, so that any perspiration you generate will be able to evaporate freely. I have found that wearing a hat, a simple wool undershirt and a flannel or wool outer-shirt is good for riding down to 30 degrees F. Adding a sweater over top, and wool socks, makes riding comfortable down to 15 degrees Farenheit for 20 mile stretches at a time.
As for seat-height, I agree (with a previous poster): adjust your seat-height so that the heel of your foot (with shoe on) barely touches the pedal when at 6:00, sitting with your hips level above the seat. Having the right seat height definitely improves pedal power.