All you have to do is put the two together...
add this to the end of what darg told ya.. Create a new "chooser" unit, thats all.
Unit - Create 1 Wisp for (Triggering player) at ((Picked player) start location) facing (Center of (Playable map area))
The only problem you will have? If someone keeps repicking, and your using the "REMOVE" style, then your gonna burn up all the heros... unless you have a lot.
IF thats a problem, then DONT do the remove stuff, and don't turn off the trigger.
If you want the repick, AND restrict the map to 1 of each hero, you will need more extensive code to keep track of which are in use, and which are not.
Best of luck.
Ryoko
EDIT1
Instead of removing the circle of power, hero , etc, maybe theres a way to just show/hide them? I am not sure.
EDIT2
If we could hash out the best way to do it, maybe we could do a super write up on this topic, with code? I'd be happy to whip something up for everyone. However, I use regions instead of player start locations. When I used start locations, I had a nasty bug where 1 wisp (teal) would appear in a totally incorrect spot, even though the start location was in the right place. Now I have 8 small regions, and it works perfect. Most people wouldn't do that though....I think