The obvious which you probably know is to avoid Marathon week (Jan. 9-13), MLK weekend (Jan. 21), President's weekend (Feb. 18). Even though you are doing a mid-week trip, some families use a Monday off as a reason to take an extended weekend visit so you might notice more crowds on the Tuesday after the weekend.
We were there the last week in January this year. With the exception of our MK day (Saturday, Jan. 27), the other days were definitely busy but manageable. Jan. 27 was crazy!!
"Your First Visit" website has published a draft version for recommended 2019 weeks. I don't know how accurate their predictions have been in the past...someone else may know. I can't post the link but you can search for it.