Ah, im guessing you figured it out by now? It might help to copy the files and put them in the correct order in a new map, and just drag them onto Skulltag.exe from there. Should work as long as the main file is left/above(depends on layout, lists, icons, you know) of the extra files.
Programs like IDE(Internet Doom Explorer) or DoomSeeker (which i believe comes with MM8BDM) should allow you to setup singleplayer stuff as well; in DoomSeeker, there's the Play Offline button close to the Start Server button when opening the Create Server window, works the same as making a server but you'll end up playing offline instead.
With IDE there's a specific Single Play tab for it which should be fairly managable as well.
The hard mode flag is found among the compat flags when making a server/game and is described as roughly "limits Pain Elementals to 20 souls", in the case of IDE put the compat_limitpain true command at the 'custom/additional parameters' area.
Oh and be sure to host GVH only with the Doom 2 (doom2.wad) iwad/game, i doubt it function at all on MM8BDM.
Edit - Links, if you need any:
IDE:
http://doomutils.ucoz.com/load/0-0-1-75-20DoomSeeker:
http://doomseeker.drdteam.org/files/doo ... rc.tar.bz2