[…] after install how does one get the desktop and apps off the usb stick and installed on the system?
[…] Does the DVD contain software that can be installed? […]
And this works on a DVD-ROM as well?There’s no further dialog(1)-driven process in bsdinstall(8) allowing you to do that.
Yes, in /packages/*/*. I haven’t attempted that, but I guess you should boot the freshly installed system, mount your USB stick, configure pkg(8) (copy /packages/repos/FreeBSD_install_cdrom.conf to /usr/local/etc/pkg/, create a symbolic link /dist), and then use pkg-install(8) as usual.