I think that it's not so much knowing that I have to be somewhere 60-odd miles away at the end of the day that might bother me, it's the thought that I might have to be at a chain of precise points by a certain time (eg at a particular place 240 miles away in 4 day's time) that might take away some of the flexibility.
On the other hand, I know that faffing about looking for accommodation in a place you don't know can be very stressful, particularly if it happens at the end of a bad day when all you want to do is lie down, cool down, or dry off...
I did JOGLE 15 months ago solo, upsupported staying in B&Bs over 16 days at the tender age of 53 and it was a fantastic experience. Just go for it - too many people talk about doing it and never make it.
I booked all my B&Bs in advance and with a group I would suggest that's the best approach.
I was averaging 10 mph including stops and did 50-70 each day, with a couple of half day rest days. So long as you set of early enough in the morning you'll have plenty of time to get to the next stopover and some spare time for sightseeing, bad weather or mechnicals.
One note of caution though about a group. There will probably be some tough days, especially if you hit bad weather and some may find it tough going. Also you're likely to have different levels of fitness. The big advantage of going solo is can go at your own pace and you don't have to worry about being nice to others in the group, if you're struggling or at a low ebb. Might be a good idea to try and get to know each other and do some training together if possible.
However, start planning (and training) now. I was staggered how much time it took to plan the route, training, get the bike just right, decide on/buy equipment & spares, book the B&B. Although with a group you'll be able to share the workload somewhat. Might even be tempted to join you - I'd love to do it again!