1/2 doz. riders, max, otherwise the pace of having everyone clear sections would slow the overall progress. Looks like your there now - certainly break it into groups of three or so if more decide to do it as the date approaches.
I'd come along just to watch or man the camera if I didn't have plans; maybe I should bring the whole family to spectate!
When Eeler and I went we had three riders, he, Trlrdr and myself; my son started to video our snail-pace progress but his battery went dead shorly after the start, so we didn't get but the first few feet on film.
Half the fun of such an endeavor is watching & helping others thru, the other half in the doing of each section on your iron horse. It's possible to boil over, dent pipes and radiators, wear down/lose knobs, rip seats and jerseys, although those gifted with appropriate skills can come out unscathed - afterall it's crawling speeds only, and something you don't do everyday, so why not? That's why when The Eel suggested we do it a year ago, we did - in spite of my new graphics/seat cover. I don't regret it, and everyone should do it at least once.