Multi-Choice Menu issues

hi
i’m trying to make a pictrure grid of assets that the user can choose from.
the limit as per now that i want is 6 choices.
once they make their choices, they hit an “OK” button then things get parsed on to the next screen.

the functionality desired here is that …

if they click on a newly chosen button.. then that button should have outline enabled and then it is added to a list.
if the list has reached it’s 6 choice limit,

…then NO action is taken when a new un-selected button is clicked.

if they click on an ALREADY chosen button.. then that button should have outline disabled and then it is removed from the list.

pretty simple.
here’s my puzzles for it.

am i missing something??
i’m not getting it to work properly.
Thanks!