Also considering dropping the mark of Tzeentch on the Daemon prince so he can use the lore of death. This would expose him (dropping his ward from 4 to 5+). Although he would still have a 2+ against direct damge spells and a 4+ against wounds from all other spells...
I would try to keep the 4+ward save mainly because:
-he is a lone model amongst an army of trolls (who have regen 4+);
-he costs much more than what Trolls do for less of a save against mundane attacks(450 vs 40(?));
-TLOS will make him difficult to hide;
-if he is warmachine hunting then chances are he will cop a cannon ball to the face at some point, a 4+ is far more reliable.
Apart from that though I like the list. Warhounds are very handy to have and annoying to face so that could be a good inclusion but apart from that, best of luck building it.