If you really want to do them right, you should run the Tyrant's list from Imperial Armor: 9, where you do over-size Legion squads of marines. That was the most telling difference, it seems, was that Astral Claws were shirking Astartes limitations on force organization, and sneaking in extra battle brothers in every squad.
And yeah, any big static defense weapons seem appropriate--a Palace of Thorns force would be backed up by every big gun possible.
Cheers.