We're frequent WDW January visitors too, and I agree with others comments.
Weather - it'll be chilly in the mornings and evenings, but just dress in layers. "Most" days will start off in the high 40's low 50's and get up into the 60's or 70's during the day. But once the sun goes down the temp will drop fast. Of course like anywhere else you can have out of season temps, warmer or colder.
Crowds - Minimal. Most rides you can walk on or wait a short time. The biggies (Soarin, Everst etc) will still have a wait, but with FP you'll be on in no time. On our last trip the standby wait for Everest was only 25 min and the FP return time was only an hr later. As opposed to in busy times FP running out on the big rides.
Rides closed for refurbishment - There is always one of the water parks that will be closed. But not a big deal since it only gets in the 70's most days. We'll still swim, but we can devote enough time to make a water park worth it.
We also have never rode the Kali River ride bc it's always down when we're there.
Park hours - The park hours should be posted less then two weeks, hopefully sooner on the TA site, but they're usually Epcot 9am-9pm, AK 9am -5pm, HS 9am-7pm and MK 9am-8pm. But since the lines are so much shorter you really won't have much of a problem getting to ride everything you want to.