Great to read you were all able to stay with the journey and celebrate together at the end.
You would not be the first group to overestimate your appetite for distance on your first big tour. I'd be shocked if that wasn't the norm.
The other classic misstep is packing too much. I recall interviewing a tourist from Japan who had decided he would come to Australia and cycle the perimeter of the continent, self supported. He began in Perth, and spent a few days riding about 120 miles south to the coastal city of Bunbury. Having got there, he realised he had packed too much stuff. Among the things he shed at that point, he told me, were his diving mask, snorkel and flippers, and "all my books".
You guys were smarter and organised a support vehicle.
I think the urge to do too much comes from seeing the journey on a car-like scale. A modern motor vehicle idles along at 60mph. The bicycle is much slower, especially when climbing, and it is as though we assume there is a loss in that. "Surely in a day on a bicycle we could cover at least 60 miles."
The funny thing is, we wouldn't necessarily approach a road trip in a car that way. "Well we should be able to average 50mph, so if we set off at eight and drive till six with an hour for lunch that"s nine hours so we should plan 450-mile days." Unless you're merely driving to reach a destination, that's not a fun way to travel. It's more enjoyable to linger over meals and take time absorbing the sights. The driving part is not the tour; it's the means to the tour.
The bicycle also can be the means to the tour. I hope you have some more fabulous trips in your future.