Yes we rented the bikes in Barcelona. There are several places that offer this.
Everyone brought their own jackets, gloves, etc, but a couple guys used rental helmets so they wouldn't have to lug them on the airplane. All the necessary gear to ride, including safety gear and saddlebags etc, was included in the rental if you wanted any of it. I brought all my own personal stuff.
We basically had a fast group and a slow group. But also you could just ride along by yourself at your own pace. We used a phone app that allows us to plan and share the routes and also see where the other riders are on a map. This let us move along easily without having to herd a bunch of cats at every intersection. At any one time we might have one dude who blasts ahead, then 3 guys in the next group, then a couple guys who decided to take a different route, and a couple more guys that stopped to get coffee and take pictures. We all ended up in the same place.
Everything was done on the fly as far as planning. We'd plan a route in the morning to some town that looked interesting, and share the route, The first guy there would find the town square or some cool place to hang out and send a message with a gps pin where he was, then we'd all eventually meet up. We'd ask the locals where a cool place to stay was and eventually go there and get some rooms. Occasionally we'd book rooms in advance with booking.com but mostly we just showed up and took what they had.
Comms for the group were done with the Signal app. A group text to keep everyone up to speed, share the routes, etc, and you could do internet calling. Pictures and videos shared among the group with an app called Photocircle, which was also super handy.
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