freshalloy.com has the most technical stuff you'll need
nico.com/240sx.org has good FAQs for all your noobie questions
ka-t.org for everything you want to know about turbocharging the KA
zilvia.net if you want to get in arguments with crazy elitist driftnuts from california/texas

lowering the car is no different than any other. 240s run macpherson strut setups, very simple once you get in there and look it over. while there are a few good spring and strut combinations that are mild for lowering and fine for street use, its recommended you get a nice set of adjustable coilovers (megan, JIC, stance, KTS, there's like 50 companies that make them) to get full use out of it, and they dont cost THAT much more than conventional spring and strut combos.

while you're looking at the suspension aspect, be sure to inspect the front lower ball joints, tie rod ends, and t/c (tension control) rod bushings (they run diagonal from the frame rails to the front lower control arms, for wears, tears, oozing goo, and etc. checking the tie rods for bends is good to look for too, and you can go over the rear bushings on the 4 arms that are back there (fronts, called traction arms, upper and lower control arms, and rears - called toe control arms), as well as the 4 subframe bushings (diagnosed by rear clunkyness).

pending on mileage youll have to replace at least one of those.

search back in this forum, and theres a few threads containing alot of links to websites that sell aftermarket 240 stuff. most of the sites i listed include sponsors and links anyways.