Just tried the block "set x-speed for actor" which I can use use for available actors and in a behaviors for last created actor or self, perhaps combining it with what you suggested above. It is like peeling an onion, one layer at a time. Once the actors are off the screen, I guess I have to kill them in order not to overload resources.
I do truly appreciate your support and when I am not battling immediate problems, I will look at your pdf, There might be things in there that I could use. I would then also revisit you website.