Definitely make ADR's if there is someplace that you definitely want to eat. If your not set on any particular place you could take your chances. I have a coworker that ended up honeymooning in WDW after her tropical destination got hit by a hurricane and because it was last minute didn't have any ADR's...she said they ended up eating alot of counter service because there were no openings at most restaurants for sit downs. January is considered slow season so you probably won't have issues but if you wanted say dinner in the castle, LeCellier, or other hot spots I would book now and you could always cancel once you got there and decided differently.