On the Stag system the plug is in the loom somewhere. Yours "might" be the same. I'd concentrate on the ability to programme and set it up, as you are, because it's a pointless exercise fitting anything otherwise. LD may be able to advise on what lead you need and if it's available publicly. Some manufacturers are fussy about who they let fiddle with "thier" software, even if you've paid for it, or not. Plug in point, lead to lap top, lap top with required port, (usb normally not an issue) software you have.
Nozzles/jets depend on what's fitted to the injectors as to what type and thread size you need, which depends on the injectors themselves. The old Stag system ran 3.0mm with a single feed vap. The newer system with a double feed vap has 2.3mm but it really needs starting from scratch and work up to a size that suits that system, to calibrate it effectively.
Copper pipe is a rather nuisance to work with, poly flex is easier by far, but needs the correct fittings. 8mill diameter.
It will run without a filter but better to fit one, or two if its duel feed, to protect the injectors. They are simple standard items and fairly cheap.
Inspection can be tricky depending on attitude IME. Both yours and thiers. You'll be feeling your way, so don't expect it to pass first off. But on the other hand they can be right picky buggers so luck of the draw really.
Tinley tech are reliable but a bit expensive, but have a word with LD if he doesn't pop in, see of Tilo the artist that's impossible to contact is about yet. Reasonable on cost and good service IF you can get hold of him.