Telecoms/Network cables are very versatile. With the plastic sheath stripped off you get very fine multi strand copper wire. I'm experimenting with single strands to fashion mudguard springs for AFVs.
With the plastic sheath left on they could work on engine pipework and hydraulic lines although it may not hold its shape as well as lead wire etc
Bronco 35087 17pdr gun crew kit has a rudimentary no 19 set included. It may not match the resin options for detail but you get 5 commonwealth figures "free"
Blu tac or plasticine will likely deform as you de-mould the master. Green stuff world's Blue Stuff is thought to work pretty well. Any 2 part epoxy will fill the mould. Not sure how they will replicate the voids though. Best of luck