"What do i need to buy for winter biking?"
A plane ticket to Florida.
If you're going to hang around Maryland, get yourself a fixed gear bike or singlespeed (easier/faster post-ride cleanup) or a junker derailleur bike. Salt, road grit and water are hell on bikes. Or ride only on clear, dry roads like I do. Even then, detail clean the driveline more often than summer if your roads accumulate as much berm grit as ours do in winter.
Clothing:
1. A couple of thin balaclavas. ****'s, Cabelas or Gander Mountain.
2. Maybe a helmet cover (I do not use one). Nashbar
3. Good thinsulate gloves, wool liner gloves, mittens or lobster claw mitts. Menards, WallyWorld or Gander Mountain.
4. Tights in a material weight to suit your temperature range. I wear tights over shorts.
5. Polypro base layer long sleeve shirts. WallyWorld Starter brand works well for me.
6. Long sleeve jersey. Lycra or wool, your choice.
7. Sock choice to suit. Poly, cotton or wool. Layer thin socks as an option.
8. Shoe covers for wind protection, road **** protection and maybe a bit of insulation.
9. Winter cycling shoes or booties...if the budget allows, they help the feet a little bit more.
10. Electrically heated socks. My treat to myself this year. Frozen toes suck.
For those stupid-cold rides that you just have to get in after being cooped up for days thru a blizzard, the heat packs stuffed into oversize gloves and into your shoes helps.
Cell phone. Changing a flat with already half-numb fingers and gloves peeled off to work is a pain in the ass.