The first sentence sounds as though it's written from a future perspective, recounting a story from the past as you suggest. It is grammatical but could be confusing as you could interpret the usage of spoke as "he continued to speak for days to come".
Replacing "spoke" with a more precise definition of HOW he spoke would help remove the ambiguity, for ...
One of the purposes of "would + bare infinitive" is to express the future in the past, and this is the correct form here.
You should say either
I didn't know that I would have to put my CPR training to use on my own uncle
I didn't know that I would have to put my CPR training to the test on my own uncle
While you could also use the "had to" ...
Both of those sentences are fine, but they would also be fine if you used the past tense:
He said that his son would graduate from college if he passed the last examination next spring.
These sentence are reported speech in which the verb has been backshifted to match the time frame when it was heard.
This also reflects the idea of perspective, in ...
Consider the following conditional declarations:
I would do it if you paid me.
I would do it if my life depended on it.
I would do it if I thought it would make things better.
The question Why would I do it? asks "What possible reason or motive would I have for doing it?
In your example:
"What possible circumstances would lead me to write I ...
We use the term conditional to refer to forms such as I would go (which is also used to represent the future-in-the-past), and the term conditional perfect to refer to forms such as I would have gone (which is therefore the perfect form of the future-in-the-past).
Resources for English language learners use therm "third conditional" to describe this sort of ...