if i am not completely mistaken you got only 1 squad being able to handle armour 13/14 vehicles... thats way to little for 1750 points
what do the choosen need a mark of khorne for? being equipped with 4 plasma (guns i guess) they are obviously the shooty type.
drop the havocs with the heavy bolters drop 5 marines of each of your 2 squads, drop mark of khorne, drop the powerswords get powerfists instead, get them 2 melters each.
rhinos do work wonders, 35 points for a transport with smoke launcher to take survive a bit longer. if not used as transports for your trops (in case you face a really shooty armie that'll kill them instantly) they can be used as a nice little wall to shelter you troops from fire while advancing.
the chaos lord really is a pointsink like this, won't get into
cc because he's too slow. if he does get into
cc he won't kill much because of shabby weapons. to stay with your (khorne)theme i would either go for kharn who's just 35 points more or take the jump pack lord shoey9797 mentioned.