My advice would be to go do a Competitive Trail Ride first and learn how to care for your horse on a distance ride. Endurance rides do monitor and take the horses P&R's. But I found CTR rides were much more focused on the rider knowing how their horses is doing. You will learn how to take the P&R on your horse, Gut sounds, filling, hydrations. Knowing how to take and monitor these will help you tremendously in knowing how your horse is doing.
CTR rides are more like a road rally. All horses have to finish the ride in the same amount of time, So speed is not an issue in CTR. This allows you more time to focus on your horses conditioning. It is easier for fellow riders to help you, since you are not slowing them down. since everybody moves at the same speed. They typically move at a slower speed than Endurance races, Giving you a chance for slower ride while you are learning.
The horsemanship judging and slower speeds may not be to your liking, So do one or two and then move on to Endurance. But what you learn doing a couple of CTRs will pay huge dividends when you compete in an endurance race.
And I'm not talking of doing ACTHA short day ride! Do a NATRC or something similar that is 40-50 miles for the weekend. Where you can really see how conditioning affects your horse.