If you are using "contingent" with its normal meaning, the idea is absurd. We can divide everything that exists into "necessary" and "contingent", one or the other? We might as well divide everything into edible and picturesque, for example. Words, but more like word salad than meaningful statements.
That there's no necessary substrate.
> Contingency means being contingent on something else
Can't it just be "luck", then? Chaos just happened to take this form.
> At some point you will likely take it for granted that there must be something that is itself not contingent
Sorry but I don't agree. I think it is perfectly conceivable that everything is contingent and there's no "necessary substrate". For example: it could be that several factors (things like the gravitational constant and the different fundamental forces) are contingent on isolation, but when they are put together the ensemble becomes necessary. Like in a tensegrity structure (not saying that I think that's what happens to our Universe, just pointing out that there's other options besides "One necessary substrate", and we don't know which one is ours).
By introducing the concept of reasons into the discussion, you seem to be adding a new dimension of purpose to it (unless you are using 'reason' as a synonym for 'cause', but if so, it would have been clearer to stick with the latter.) Your belief that the universe has a purpose (if that is what you are saying here) does not logically compel anyone else to accept a first cause.
Update: In your view, there is a hierarchy of causes of something, the first of which is necessary and the rest of which are contingent. Therefore, the second cause was contingent. This implies that the first cause made a choice between which of the second-cause options obtained. But as the first cause had a choice, then it could have gone another way, so it was contingent...