Weather is a complete crapshoot lol. It could be beautiful, it could be freezing. One thing is for sure, it wont be 100 degrees with 200% humidity like in the summers here so that is always nice.
As far as ride closures, its rumored that Twister will be closed for good by then but this is not confirmed. Typically at least one water ride is closed at this time for annual maintenance in IOA, I would guess Popeye...they may have two closed, but considering its MLK weekend they may only try to have 1 down. Other rides are subject to annual refurbishments during the off-season but this schedule is not set in stone yet as far as I know.
Also, even though January is typically verg slow, MLK weekend can bring out lots of locals and weekend-trippers...dont expect lowest-of-the-low crowds. That being said, you still should be fine and the park will not be completely slammed.
Have a great trip, and feel free to ask anymore questions!