The lord is too many points for too little bang. S3 lightning claws
With GK there get yourself a GK lord. Nasty by far for not much more.
Get much more anti tank in there.
By DH with WH allies instead of vice versa you limit the anti tank you have.
storm bolters on sisters is not a good look. especially in standard squads
teh seraphim need a VSS with evis
this list on its own is to be honest not very good. It doesnt excel in any area and teh weapons kit outs on teh sisters in not good.
EDIT: sorry that sounds damning.
Try a cannoness HQ
GKT elites
2 rhino sisters squads troops
1 GK squad troops
1 GK squad Fast
1 seraphim Squad Fast
1 melta/ flamer dominion in immy fast
exorcist Heavy
Heavy bolter Retributors Heavy
kit sisters book of st lucius, and melta weaponry.
This way you will have a balance between firepower (sisters) and CC GK