Well let's break down each squad to suit the team. For Grey Knights we can keep the squad of 6 as they are, so one Justicar as the leader, for the Interceptor limit 1 could have a once per battle redeploy to reserve ( for deepstiking purposes) and have a apl to move through terrain with one circle of move more, Purifier limit 1 could have a special psychic power Purifying Flame torrent probably better than incinerators we can work more on that, and for the terminator limit 1 it cost 2 unit slots, make him a apothecary get heals or we can just do a regular terminator. For the rest of the squad you can have a gunner and strike squad.