[1] has been well covered above.
[2] No; I haven't used a Classic Swede spring kit. But 4 inch lowered on a 164.... given the state of the Midland and Bass highways - nah, I wouldn't do that. What works fine on the M4 west of Reading IMHO won't work very well west of Launceston, like where the road gets very rough around Elizabeth Town. Take into account also how you'll be going on and off The Barge when travelling interstate, which means dealing with those ramps on and off the ship which have some steep angles. Especially into Deck 2.
According to the (Green) book, standard spring rates on a 164 are about 511 lb/in front, and about 112 to 117 lb/in at the rear. My 144 has springs cut by the PO and is lowered about 2 inches, and it's not happy - too soft, and somewhat low for dealing with domestic street use. I do have a pair of lowered Kings 164 fronts to go into the 144, which should firm it up somewhat while raising it a bit, but I want to get the spring rates measured before I do.
IMHO, if you want to lower the car, you might be better off going for the 40mm lowered set which Classic Swede also offers.