I often encountered Doomers (and Hexeners for this purpose) which were already stuck. Apparently, I found myself that the first hub, Seven Portals, is relatively easy, (Thou only after you used a handthrough for three times from the 'net.). It's like a good place to put this in here <dumb>.
The mission can be split up in the following parts:
Left side, middle door - G.o' Ice (Guardian of) - open GoFire/GoSteel doors
Left side, near door - GoFire - acquire Flame Mask (+ hit puzzle switch)
Left side, far door - GoSteel - two puzzle switches
Right side, mid - GoIce - get fire and steel keys
Right side, far door - GoFire - use key and hit puzzle switch
Right side, near door - GoSteel - use steel key and hit two puzzle switches
Left side, mid - GoIce - enter right side (ice), solve puzzle on steel/fire
Left side, mid - GoIce - enter left side (steel), solve puzzle, returns you to GoIce.
Return to 7 Portals and enter the exit door.
In the last part, I had to use the Chaos Device (Teleportation to Level Start). Also, in the last part when you return to GoIce, you usually have to kill monsters to lower the walls you're in; I used a noclip here (kthx). Back on Seven Portals, same procedure, kill monsters to get to the Exit Portal (used 'fly' cheat, kthx2).
http://linux01.org:2222/f/7portals.lmp - ZDoom 2.0.60.
I am quite sure I have an older Hexen IWAD than the latest, hope it doesnot mind.