Manuel
What caused any given event (ie reality-which is a specific physically existent state of whatever comprises it) must fulfil certain strict criteria, because physical influence cannot 'jump' physical circumstance. That is, in terms of order, any given existent state cannot be the cause of another unless it was the predecessor in the sequence. While in terms of spatial position, it could only have had physical influence if it was adjacent to the position now 'occupied' by the resulting effect, because alteration in spatial position is a difference (ie another reality). And as with any difference, this can only occur 'one degree' at a time. [What constitutes a 'degree' for any given physical attribute is irrelevant to this generic argument]. The point is that either something remains in one existent state, or there is a difference, and difference can only occur in discrete existent stages (a 'degree'). To put this simply, if the two spatial positions being considered are not adjacent to each other, then there were other spatial positions in between, and whatever physically existed must have been in each, sequentially, to be where it is now (the differentiation of spatial positions being a 'degree'). This simple principle applies to any physical attribute.
Now, the other point revolves around what caused the alteration which results in one physically existent state being superseded by another (both of course do not co-exst). That cannot be something which is physically disconnected with what occurs. Neither can something have physical influence and not be physically existent. Indeed, it must be what occurs.
In other words, the whole way in which we conceive reality is ontologically incorrect. There is a tendency to conceive in terms of objects, when in fact what physically exists at any time (the reality) is the physically existent state of whatever comprises it. And there is the concept of something else having an effect on the object, whereas this can only be whatever constitutes what is being wrongly being thought of as the object.
That is, either there is ultimately an inert substance (which could occur in different types) which 'carries' the 'properties' which are the determinant of change, or the 'properties' are themselves the ultimate substance in our reality.
The key to all this is the realisation that any given reality is the physically existent state of whatever comprises it. Then the rules as to how the sequence must occur, etc, are easy, in generic words! In practice, how this manifests is extremely complex and beyond our ability to differentiate in experimental mode. The degrees of alteration and duration are vanishingly small. Apart from anything else, in the context of sight for example, we are dependent upon the ability of light to comprehensively and accurately capture and transmit all that occurs, leaving aside our ability to decipher all that if it did so.
On your question: "Also how do we obtain an initial causal event, that being an event that did not exist until it does?" There can be no answer to this, because it transcends our existence. We just have to accept that whatever is demonstrably the start point for existence as knowable to us, is the start point.
Paul