Blog/Event posts don't seem to have attachment options so OneDrive link seems to be the best option. Use the same link for permission forms and other files and use them for web pages and event posts.
Blog vs Calendar
- There is an iPhone app for Squarespace Blogs. None for calendar and editing on mobile browser is not so easy.
- Calendars can show in grid view, but user cannot choose to switch to list view (like this blog). You also can't print the grid view (it is cut off).