By the steps you provided I built what I think you want.
As The Mighty Atom and Mazetar pointed out it really is all in the timing.
I'll try to walk you through it:
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Map loads -> trigger_auto fires "mm" (
NOTE I didn't use the "Level Fade In" in the map properties, mainly because I wanted to force the timing and didn't know exactly how long its fade's duration was. The side effect of doing what I did is a quick view of the map on map load and then it triggers the fade. This could be fixed by either starting the player in a dark room and teleporting them before the final fade in, or ignored.)
Time t = 0s:"multi_manager" mm is triggered.
"env_fade" mm is triggered (
NOTE The mm isn't a type-o.)
----> Properties: Duration = 5 seconds; Hold Fade = 5 seconds; Flag: Fade From is ticked.
"func_wall_toggle" w1 is triggered (forces no movement throughout)
Time t = 5s:"env_fade" mm starts to fade in.
"trigger_camera" cam1 is triggered.
----> Properties: Hold Time = 15 seconds
Time t = 10s:"env_fade" mm is done fading.
Time t = 15s:"env_fade" fadeout1 starts to fade to black.
----> Properties: Duration: 5 seconds; Hold Fade: 5 seconds
Time t = 20s:cam1 is finished
fadeout1 has screen completely black and holding for 5s.
Time t = 25s:fadeout1 is no longer active.
"env_fade" fadein1 is triggered.
----> Properties: Duration = 5 seconds;
Hold Fade = 0 seconds; Flag Fade From is ticked.
"trigger_camera" cam2 is triggered.
----> Properties: Hold Time = 15 seconds
Time t = 30s:fadein1 is done fading.
Time t = 35s:"env_fade" fadeout2 is triggered.
----> Properties: Duration: 5 seconds; Hold Fade: 5 seconds
Time t = 40s:fadeout2 is done fading and is now holding.
cam2 has finished.
Time t = 45s:fadeout2 is no longer active.
"env_fade" fadein2 is triggered.
----> Properties: Duration = 5 seconds; Hold Fade = 0 seconds; Flag Fade From is ticked.
Time t = 50s:fadein2 is done fading.
w1 is triggered again releasing the player.
End.
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The entire cycle takes 50 seconds to complete from map load to finish.
Here are the .bsp and .map files. If it is indeed what you wanted feel free to just rip the entities and utilize them as you wish. Be careful though of changing the timings as each entity's correct timing depends on what's triggered before it.
BSP:http://sites.google.com/site/nefariousparable/downloads/fade.bsp?attredirects=0MAP:http://sites.google.com/site/nefariousparable/downloads/fade.map?attredirects=0