Early January is usually a slow time in Florida. You shouldn't have a problem finding availability. Last year, I had no problem getting a unit in mid February. It just took a lot of patience and something eventually opened up.
There is a chance that a three bedroom unit may be available. This would be ideal. All two bedroom units should be fine. The fifth person may end up on the sofa in the livingroom. My unit at Fairfield Cypress Palms had a king size bed in the master and two queen size beds in the second bedroom. Some resorts offer two double or twin beds in that room. The 2nd bedroom also had its own TV which is not standard in every resort.
Do some reseach on each resort that comes up often: Silver Lake, Cypress Point & Grand Villas, Vacation Villas at Parkway, Fairfield, etc. and decide which features are most important. Check out the floorplans and driving distance. If you like to eat offsite, review options for dining nearby. Read the reviews on tripadvisor.com to see what people liked and didn't like about their stays. If you do your research now, you will know what unit you really want and be able to grab it as soon as it becomes available.
I hate driving, so I always choose resorts closer to WDW. Summer Bay is too far away. I always book a two bedroom unit so I know I will always have a big jacuzzi tub and washer/dryer in the room. Condos are the way to go, IMHO.