As an old bicyclist, I've got a bunch of bike gear that I'm reusing.
Generally if your 'core' is warm, the rest is tolerable, but I do see that as it gets truly cold, I'll want to improve the warmth at the extremities. So I wear a pair of long riding pants under my jeans or docker's. I have a couple pair, the warmer ones with cotton/lycra blends are too much for the 50's, so I'll keep them until it's in the 20-30's, and use the all lycra ones for the 40's-60's. If I determine that's still not enough, I'm looking into a
http://www.scooterskirts.com/ to cover the legs when needed.
For the upper body, as always, it's layers. Again from the cycling days, I'm reusing some old reliable gear. UnderArmour long sleeve shirts under whatever I'm wearing that day. Frequently it's just a Mock turtleneck or old navy fleece hoodie, but it also works well under an Oxford cloth button down. For colder days, I could easily use a flannel, or heavy sweater. Over top of that, I always wear my leather riding jacket, that I bought a touch big for this very reason. For damp days, I also have an oversized fleece lined rain coat (Totes, $20 off Amazon) that I keep under the seat for an added layer against the moisture and wind, it's just big enough to slip on over my leather riding jacket, and cheap enough that if I hit the ground, I frankly don't care about the $20 rain coat

.
I wear a full face helmet, and have a windshield, so I don't find I need anything around the neck, though I could see wearing full turtlenecks fairly often if needed.
Hands and Feet are an issue for alot of people. During the warmer weather I'm using some Icon patrol gloves, but I can see them being 'not enough' at 60mph when it's 30 degrees out. I've seen some good leather gloves, but I REALLY prefer the feel of the lighter gloves, so I'm trying to convince my sister in law to custom make me some leather gloves with heavy top leather and leather reinforced lycra on the palms and inside fingers. the old ones I made like this for my mountain bike are completely abused, bordering on trash.
Feet though, this is wear any hiker's in the group will have the best advice. Again, layers, and good socks and boots are your friends. You could go with good riding boots, but I generally don't, I *am* commuting to work and do have to look nice, so I've taken to wearing good socks with my various shoe options. For casual days, I like
http://www.skechers.com/catalog/browse. ... rodId=7698 as a good mix of form and function. On dressier days, I've got some
http://www.skechers.com/catalog/browse. ... rodId=7764 that aren't as stout but provide a little extra ankle support and reinforcement, just in case. Most of the vendor make varieties like these for both men and women.
Socks are a huge issue though. Cheap generic socks are virtually useless when it comes to form and function. I long ago quit buying the cheap socks you find at shoe stores. Hiking socks are where it's at. you can get nice looking socks that are engineered for warmth (or cooling) and moisture control. Both things that are important to the scooterist

. One decent source that I've used is
http://www.sierratradingpost.com/lp2/hiking-socks.html (they also have boots).
I know some sport bike riders that also swear by thermal underwear and older ideas like that, but the advantages of lycra and lycra blends is twofold. One, they prevent most fabrics from sticking to them, and two, if you hit the ground, they become an extra layer of protection, as I can personally attest that Lycra is a better protector of your skin than cotton or nylon.
Anyways, I know this is long, but these are just my thoughts and experience. I'm also in uncharted territory for myself. I've biked year round for almost 20 years, but this will be my first winter scootering in the cold weather.