if you're cycled all but the most picky of fish should in theory be fine to go straight in. certainly i wouldnt be concerned about putting barbs in. will also give them time to sort out their pecking order before putting other fish in. the danio thing, ive seen 4ft being banded round the forum as the benchmark for danios, thats all im going from. ive got a couple ive rehomed from a friend in a 2ft tank, and they really need to be in a bigger tank, they are very active.
my knowledge is far from the be all and end all, but im repeating what ive seen said on here. if you're cycled, theory is you can 100% stock straight away, though in practice its much better to gradually do it, but not too gradually as bacteria will start to die off if the ammonia your fish produce is less than the ammonia you have been cycling with, as the amount adapts to how much food (ammonia) they have. if i was you (and iw as stocking it), id probably put the barbs in, couple of days later the tetra, couple of days later the cories, then the gourami (only as i never have much luck with them), then the plec, as you want to be sure things are good before you start putting expensive fish in there.
then id throw a couple of banjos in there and forget about them until one day you see their heads popping up out of the sand. funny times..........