Not sure it's a helpful guide, but my story:

I don't bike tour. It hasn't cracked the priorities with spouse, 3 kids, job, and limited vacation time. I live vicariously by dropping in on the forum.

I did one tour when I was 16, a three week 1000mile tour around Lake Michigan organized by a YMCA. It was guided but unsupported. We carried all our camping gear, stoves and fuel, and basically bought food once per day.

They sent out a 5-week training plan, going from 5-miles on alternate days to 25 miles every day, then welcome to the trip with loaded days of 45, 55, etc. Biggest scheduled day was 93ish miles.

I had camped, packed for backpacking, and camp cooked (&cleaned, the harder part) as a Boy Scout, so that aspect was smooth and fun. And the training was enough, there were harder days but I was never suffering.

Unfortunately, of the original 2 guides, five boys, and five girls, two of the girls hadn't trained enough (and perhaps had a very wrong idea what the trip entailed, language barrier?) and decide to quit and bus back to the YMCA site.

I dreamed of being a CIT or something on future trips, but the next summer I worked all summer. Then we moved, there was nothing (organized) that seemed similar.

And time got devoted to other interests.

Maybe when I retire!