i wouldnt add more cichlids in a 4ft long tank. once that GT hits 6" which doesnt take long then it may become an ass plus you want your centre piece in tip top condition which fighting for territory doesnt do. after 6" you begin to realise that a 4ft long tank isnt as big as it first seemed.
i would go a small pleco such as an albino bristlenose, they work hard and look great.
also pictus for cleaning up the bottom a little and giving more activity, this and the dollars you already have will help your GT to come out of his shell.