Only just saw I got some PMs. I am not on Atarnotes often and just don't notice the messages most of the time, sorry about this. Will just try to answer the questions here:
I heard before that the subsequent offers may arrive on any days / weeks this month. Say some people already declined the offers this week (to some it would be too far, and some others took the exam as an experiment to find out where they were), then those places would be re-offered as early as next week.
There can be a chain effect. If some places at macrob / mhs are made available and offered to people who got offers to the other two schools in the first round, then some spots in those two schools will come up.
As to PD, I agree with what was mentioned by others here. You want to show your abilities and passions in other areas. Like, while being a good academic student, you are also genuine on interests to a number of other things.