I like the idea of the DA, since they tend to melt MEQ fairly well. You will be facing a lot of Grav though, and quite possibly a few Grav Bike lists who can run circles around the DA and just Grav you to death.
Because of this, I would keeping the DA as lean as possible. So keep the Spirit Probe, WWP, and maybe the Sump if your (black) heart is set on it.
Otherwise you will need units to "pin" bikes in place. Your reavers can do this, but will not be able to traid blows for multiple combats with only units of 3 (SM bikes generally come in units of 5).
I generally like the HWB on the scourges, but they are not a stand alone unit. They are good at stripping the last few HP off a vehicle, but not taking things out on their own. For utility I would recomend the Heat Lances, since they can KILL vehicles in one volley, and also take out 2+ armor (which only the DA can really take on).
Thats my $0.02 anyway. Certainly a good start. I like the mandrakes for objective grabbing/ harassing firewarriors/necron warriors