Here you can download the pre-built executable of BasicBox, and it includes the required roms folder.
There are also two sample hard disk images available here so you can get started using it immediately. There's a full FreeDOS 1.4 installation sample, and a Debian GNU/Linux 2.2 "Potato" installation sample. Extract either or both of them into the same folder you extracted the executable, navigate to that folder in a command prompt, and type run-FreeDOS.bat or run-potato.bat
The bat files will launch BasicBox.exe with the proper command line options to use these disk images.