Well why not use more bits from the tomb kings? There are here and there some nice decorations. They also have scarabs so you don't need to sculpt them all from
GS.
Then you could add different shoulder guard and tabarts as well as scrolls and gemstones.
Maxmini, kromlech, puppetswar, anvil industry and chapterhouse studios are all making parts that could be used for your scarab occult like shoulder guards, heads and some other stuff.
And additionally here are some pics from dakka to fuel your inspiration: