No obvious certification reasons.
O-Wt landing would not be higher than max takeoff wt; brakes etc are certificated and tested for max wt RTO. Thus brakes and tyre care is not an issue; your are not going to have a quick turnaround !
Time wise; land as you judge the urgency of the situation; according to the situation as assessed, at that time by the people there.
Weight; reduce wt to maximise safety as judged by the landing distance margin vs possible need to make several approaches / divert. Don’t box yourself in to making a ‘first time’ approach and landing which probably has ‘not be done before’ - simulator may not count for much in a real emergency; the aircraft may be the same, you are not.
Dump for the ‘environment’ ! Only if woods / wild life, fish stocks, or fuel tanks are in the overrun area.
Relatives will not thank you for planning a ‘Green funeral’.