Siestas are the one thing I miss back in the time I worked in a country that observed them. Nothing better than having a cup of coffee after lunch, taking a quick nap after, and waking up just in time for the caffeine to kick in. If I do that at my work now, I’sd probably be fired for sleeping on the job.
Assuming your group has a considerable amount of non tech savvy people, I would suggest Friendica just for the familiarity, since it’s supposed to be like facebook and it would be easier for people to use. I don’t know if it has groups though. You might also sacrifice admin/mod capabilities. I’m not familiar how good friendica’s admin tools are (if any).