Since I'm still playing around with Warscrolls the concept of building the models is playing on my mind a little bit, I'm pretty happy with my concept for the labourer centric units so have moved on to considering the Phalanx and Ironsworn Units. Below are my current ideas on units and their composite parts:

Weld Arbalesters/Riflemen - 
Bodies/Legs - Necromunda Cawdor
Heads - Human, Bare (currently looking at Van Saar head upgrade kit)
Weapons - Crossbows from the Empire Crossbowmen kit, Rifles from the same kit of the Skitarii Range Rifles.
Additionals - Power/Shot pouches made from greenstuff, more ornate heads for the Quartermaster and Master of Shot (thinking forgeworld Ironsiders heads)

Weld Phalanx/Other - 
Bodies/Legs - Militarum Tempestus Scions (if considering armoured look, Cawdor if focusing on the more Labourer aspect)
Heads - Nuln Ironsiders
Weapons - 1.5mm brass rod cut to 7cm lengths as pikes, the Van Saar energy shields with the hole replaced with a duardin icon and painted to become a far more primitive shield instead.
Additionals - Open to suggestions.

Ironsworn Templars - 
Chassis - Starting with the Forgeworld Ironcircle model as a base, bore a column vertically down the front of the model to craft an alcove for the pilot, removing the neckpiece in the process. Within this cavity mount the pilot (Captain from empire Steam Tank kit), using greenstuff to sculpt the crude leather straps of a harness.
Pilots arms should stick out horizontally, disappearing into the chassis frame to control the suits arms with legs strapped and supported by metallic pedals below.
Power source - Do not add the top armour to the chassis, instead utilising the steam engine from the Empire Steamtank kit, cut the barrel in half and mount over the top of the chassis forming a rudimentary top piece.
Armour - Leaving the shield and shoulder pads off of the Ironcircle, take the rear wheel frames from the Steamtank, cutting each in half until you have 4 semi circles of banded wood. Attach two of these to each of the shoulder frame mounts to make crude wooden armour panelling over the shoulder.
Weaponry - Angling the hammer to be held in two hands (as the shield will not be attached), replace the hammer head with a suitably Age of Sigmar weapon of your choice. Alternative weaponry build takes the Steam Cannon from the Steam Tank Turret, mounting it on the haft of the Ironcircle hammer and running hoses (made from greenstuff) to the steam engine on the armours back, this gives the suit a short range steam belcher.