Hello Steve,
There is a large measure of agreement that time, space, energy (that you refer to as 'action') and matter are fundamental constituents of the universe.
I thought that there was also general agreement that 'aether' is a misconception.
Regarding your references to the 'shrinking universe' and an 'expanding universe', physicists are inclined to define the universe as the realm of all-that-they-know-exists (expanding or otherwise), but are not inclined to speculate what lies beyond.
The concept of 'universe' is singular insofar as the prefix 'uni' refers to there being just one realm that is constituted to include all-there-is, including all that we are not currently conscious of.
I beg to differ with you regarding your statement that 'it is from discrete events that the notions of continuous space and time emerge.' Discrete events arise from the interaction between energy and matter. They are enabled by the prior existence of time and space that function as context. Only increments of time 'emerge' between events, which fact helps us distinguish each event from all others.
The issue of knowing 'why' energy and matter 'are the way they are' is an improper question unless one acknowledges that they are so because mankind has categorically defined them that way. It is important to recognise that energy and matter are in an on-going state of transformation from one form to the other dependent upon circumstances.
While time separates events as I have noted above, the only time that is 'real' in our experience is now, now and now.
We must be careful not to be unduly persuaded by professional jargon because there are differing interpretations of what it 'means', and the use of esoteric symbols and equations is a sure way of diminishing comprehension by a 'well-educated but non-specialist audience.'
Your opening question 'Do all things necessarily emerge from a few fundamental things?' is self-answerable, and understandable, if you delete the word 'Do'.
There is no reason to attribute rationality to the universe. It is mankind that is rational, a function of consciousness, and strives to reduce all other phenomena into conformity through rational analysis and categorical packaging. That is our self-made 'reality'.
Rest assured that I am fully in accord with the title of your essay 'Discrete Matter and Action (energy) as (being) Fundamental'
You carry my best wishes for good luck Steve.
Gary.