Platies are very easy to keep 2 males 6 females would be your best bet otherwise the females will get stressed by constant advances from the males. Still ike the gourami idea and will be very curious to see if it works out. Keep way more females than males. good luck
For the platies the males and females are equally as colorful. For the gouramis the males tend to be more colorful. One way i sex the gouramis is to look at their fins. if they are rounded at the ends this indicates a female. If they are more pointed this indicates a male. However, if they are young they all look like females. HTH