Fantastic report, I really enjoyed it and am looking, even more now, to returning to that area in April next year.
On a route note, I think you missed out on a fabulous end to the ride by not taking the Vies Verde from Olot to Girona. Although it is an old railway track re-purposed as a bike (and walking) route, it's surface is well graded, there are plenty of refreshment stops (apart from, note, on a Sunday) and has ZERO traffic.
As for organising a large group ride over there, it will, probably, be harder than you think. The first time I went I was solo, the second time with one other and next year there is going to be three of us (unless I can persuade any others to join in*). Small groups is the way to go, especially if you are of a similar ability. Any other advice would be superfluous as you know all about group rides (organising cafe stops, sleeping arrangements etc).
*At the risk of breaking the rules, there is a thread for the trip next year, entitled "El Segedors"**, over on the other forum that starts with Y, if you are capable of covering ~300miles in 5 days, and are not afraid of UP, then it could be for you! .
**Ask a friendly (in my experience, other than the odd taxi driver, they all are) Catalan.