going by the 1" of fish per gallon "rule" you have around 27" of fish in a 28 gallon tank (i have taken a figure of 2" per gourami), plus your plec.
Not sure how big the plec grows too . maybe someone elso could helpin thsi regard.
As such you seem to be fully stocked, if not a little overstocked, but so long as you keep a proper maintenance regime, and your filtration is good enough (and on the proviso that your plec does not grow too big!) you should be ok but i would not think of adding any more fish.