You should be fine for Polybians then. Mind you, most of the Polybian units have the same names as the Camillian ones, but slightly different stats. There is no battle requirement for the Polybian reforms. As you say you have improved barracks after you qualified for the Polybians, you should have them available to you.

You could try to destroy the barracks in a settlement (for example Roma), and use the process_cq cheat and add_money cheats to quickly build up the barracks again at no cost. See if you can get them that way.

Once you activate the background script, the "talking head" is supposed to disappear. What do you mean you have no text in the script? The talking head is not saying anything, or the script file ([Total War installation folder]\EB\Data\scripts\show_me\EBBS_script.txt) is empty? It can also happen that the activation does not kick in properly when loading a saved game. You'll immediately notice it, and the talking head will pop up again once you select a city.