Just two little things quickly

That law did not originate but only regulated the already existing custom of slavery ( Exd 21:20,21,26,27; Lev 25:44-46; Jos 9:6-27). Slavery was however--authorized; it was regulated by the Yovel--the jubilee. This set each man woman and child free--or provided the possibility to be free.

Multiple wives--BAD IDEA--ie Killed Solomons kingdom--but was never particularly forbidden. Yet Yeshua pointed out
G-ds plan was one woman-and one man--two made into one.
Abraham and Sarah is the model. One man one woman--this is Torah's standard--yet it made provision for the hardness of man's heart--as it always does.

So the truth is that NO PART, not one jot or tittle are not valid today. All of the Torah is still valid and we must follow it