u need more troops especially hormagaunts also drop the without number and scuttlers on the gaunts. tyranids are a swarm army u need lots of cheap troops and big scary monsters. so get a carnifex.
if u have a budget problem use the hormagaunts that u got with your gaunts make them cheap though, so i would say use everything u got in the 2 gaunt boxes 16 gaunts and 16 hormagaunts.
your genestealers are also pricey cut out the scything talons its over kill in 750 pts list, but definatly give them extended carapace.
i wouldnt take two zoanthroapes, one should do it if u use it right, they are good but again this isnt a huge list
definatly try get hold of a carnifex always a good thing, but just make sure u keep it cheap i would suggest a Dakkafex 2 devourer, enhanced senses, 113
so ya thats what i think but troops are the main priority then the carnifex. good luck
sparky