You have a lot of support choices but they are almost all very static. I would advice to invest in a vyper or two to get a mobile heavy weapon. then add a second guardian squad of a small size and a BL.
Personnally I would add a serpent for the dragons and perhaps a HtH specialized unit...
And take big black guardians units. (When I use Ulthwee, I take 2 units of 19 guardians (19 defenders with warlock and grenades+ 19 stormies with warlock and flammers and grenades). I let the support platforms in normal small sized guardians squads.
againsts nids, thes combo are awsome. against necrons, I would say add one or two singing spears and focus upon killing the warriors. as HtH specialist I would say scorps.. The avatar is perhaps unecessary here? (I don't like it so my opinion is perhaps biased)
