I would like to be able to use USB drives on the network with read and write capability like these new consumer routers do these days. I do not see this in the web GUI or its very well hidden. I would like to have NTFS support and Fat32 would be fine and most Linux filesystems would be nice too.
This feature is not in OPNsense and is not on the roadmap, for a security product is probably not a very good idea to use it as a NAS.
I can recommend FreeNAS http://www.freenas.org/ or you could delve into how to set up SMB/NFS shares with FreeBSD on top of OPNsense https://www.freebsd.org/doc/en/books/handbook/network-samba.html / https://www.freebsd.org/doc/en/books/handbook/network-nfs.html