I don't have a Kimberley Northern, although care for Eastern Blueys is similar.
120cm/4ft is a nice size for an adult, Blueys will happily live in an adult sized enclosure from a young age. My Bluey is in a 120cm L x 45cm W x 60cm H enclosure. His next enclosure will be 15cm wider, as he's almost 40cm long.
32-33 degrees celsius basking spot is generally acceptable for most species of tiliqua.
Standard spotlights from Bunnings work a treat, I use a 40w Phillips focused beam, with a tile underneath. Wattage depends entirely on how far away the bulb is positioned. If within reach of the skink, ensure it has a cage over it.
There is no best substrate, as people prefer different things. I haven't had any trouble with Kritter's Crumble in the coarse variety, my Eastern, Gizmo, loves to burrow and bury himself under it and it reduces smell associated with feces well, I clean them up as I see them, though.
It's debatable that they need UVB, however I have used a UVB 5.0 in the past. I'm not using any at the moment, although I am supplementing with Calcium and vitamin D3, plus multivitamins. Calcium and D3 gets fed every other feed, multivitamins get fed every fourth feed. Gizmo gets supervised outside time at least three times a week, usually five pending good weather, for 10 mins to 1 hour each session.
I've only been keeping a Bluey since March this year, so I do not have half as much experience with them as I'd like. Thus, it would be ideal to get multiple opinions and compare them to each other before coming to a conclusion in regards to their proper care.
Best of luck with the Bluey, they're a fantastic animal with unique personalities - certainly my favourite out of the reptiles I own (don't tell my Jungle python that, :lol
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