Maximum distance between access points?

I volunteer at a local non-profit farm / historical site that currently has "Legacy Open Mesh" products that are no longer supported (look at datto | networking.) The network was being managed remotely and there is no local support for the current products so I'd like to have something we can manage locally.  The site has 6 major access points, two in a barn that houses the modem and router from Xfinity, they aren't a real issue, 1 at the  Sugar House right next door, again no real issues. The issue is at the remote buildings, a restroom that houses 1 of the access points, about 35 yards away (to help cover an open field) and  2 access points in  a pavilion about 75 yards away from the barn.  I installed a line of site wireless router from the barn to the pavilion so I do a strong signal there.  The issue is getting off the older equipment and onto something that will cover the above mention area PLUS the field in between for events, like Artisan markets where the vendors want access to WiFI for transactions. The mesh solution seems like an obvious fix since I can set up a secured network (security cameras and the like) & a guest network for the vendors.  I was hoping with the mesh, I could hop from one access point to another cutting latency down to a minimum.

Any suggestions welcomed.