@jgrubbs: Thanks for reaching out and asking these questions.
Is there a way to retrieve all entries in a Journal, or at least force it to deliver a more than whatever it chooses to give me?
I know I can limit the size, but I want to do the opposite.
Currently this is not possible. See this and this in our FAQ section.
Also, is there a certain optimal cadence for querying the Journaling API? Once a second, once every hour?
The cadence should ideally depend on the rate of events that are being published against your event registration and how fast you would want to catch up. We also return Retry-After headers with 204 responses, so the best thing would be to follow that.
Hope this information helps.