You could use the Hands of an Phantom Droid from the Eldar for the Hands of your Suit.
I have tried it myself, looks not bad and the Plasmagun looks like a Pistol or a real Gun in it.
The Fist can be used for an Energyblade or a Close Combat Motive and the other two open Hands...
One with a Shield and one with a other Weapon, for Example an Armored Core Laserblade?
The Backpack looks like an Space Mobility Upgrade or a landinghelp for Airborne Missions...
But there could be some Packs for the Parasuits on it.
Or a high Mobility Backpack for high speed Missions.
Or or or. There are many Suituations where such a Bigpack could be Useful.
But, don't make the Error and make the Suit to Gundam Style. Heavy Gear or Front Mission Style is more interesting for Warhammer 40k.
(My personal Plan for my next Crisis Conversion is to make a Battletech Mecha out of Crisis Parts.