Good luck, though. I believe first-hand experience with living a self-determined life - including online services - aligns nicely with scout ideals. And trying to convey the media-literacy that allows people to make informed choices.
And I can see some benefits with having documents available to everyone, templates, and collaborate on the paperwork...
Glad to hear other groups in the area have success with Nextcloud... Another idea would be to somehow unite and share the hosting bill for a slightly bigger Nextcloud... But I still think the old laptop idea might be promising to get started... depending on the network situation in the building and whether you can configure port forwards and all the things that need to be done. Just make sure to have some kind of backup strategy if you put documents there. Can't be too hard, as Nextcloud is made for syncing data... And I wouldn't put personal information about kids there unless the admin knows what they're doing. But there's plenty other stuff to put there.