tiger barbs need to be kept in a minimum group of 5, pleco is gonna get bigger than 6inches if it is a common pleco, watch out for aggression from the gouramis towards eachother, the mollys will probably breed, and those sharks you have are not supposed to be kept together, they are very aggressive towards their own species, 1 in a tank that size is good. if your tank has been only up for a month are you sure it is cycled completely?