try using the calendar. even you cannot set an number of Tracks after which your ID will come, but you can set a timespan after that the jingle/ID should play.
the average track is about 3:30min, so 5 tracks would be ~17:30min
This is how my event for my jingles Playlist looks.
<playlist loopatend="0" shuffle="0" priority="1">jingles</playlist>
Thoughts: setting the "duration" of this event to smth. smaller than the shortest track in your jingles playlist AND setting random to "1" should play only 1 random track from the playlist. (this is untested by now)
how's the Progress on a new beta build?
at least the fix for the "bad-chars" (äßüö... non english chars) would really be nice.