Isn't it good idea to detect already installed (not runned) ASes and check
configured ports or at least make a suggestion to user to check ports' numbers
twice before installation to avoid future conflicts?
Very-very valid. And not a difficult task.
A warning "banner" should now appear is at least one of the installed GlassFishes
or SJSAS'es is using one of the selected ports as its http/https/admin port.
That's the best we can do at the moment.