That's a really interesting list that you have put together there, it would be an enjoyable challenge to play I'm sure.
If I was going to analyse it, I'd start by looking at a few things:
Weight of fire: The Basilisk has a minimum range, and at 500 points (esp. against grey knights) you can bet your bottom dollar that you'll be spending most of your time not firing that earthshaker cannon. Sad, but true. Consider looking instead at hellhounds or a leman russ to pump out the armoured support.
Lasguns - you have a fair few, but they won't last long if you are planning on leaving them in the open. You are going to be relying heavily on finding cover for those two squads of veterans, because without peons to fend off terminators for a turn, you won't be seeing much use from those awesome autocannons. Consider dropping frag grenades since you probably won't be seeing much use from them - if walkers or assault troops are that close, you've probably died anyway.
Melta HQ - a powerful unit that can really unleash some pain, but if you send it out hunting you can be sure that you are giving away slay the warlord and not getting much use out of your orders.
Cover - as discussed, you need cover for the veteran squads. If you can find points for an aegis line, that should save the bacon for one of your squads.
Refractor fields - ok, if you like. I think these are a bit pricey, especially considering that the Company Commander already comes with an invulnerable save. The psyker will not have that save pay for himself if you tend to perils a bit, because all perils of the warp wounds ignore invuln saves as well.
Medic - I know they seem good, but T3 means anything s6 will end them, so close combat with grey knights, shooting from eldar and a strong breeze from tau will make your medic just a waste of points. Still, helps against bolters and necrons, so up to you.