installing abshow much overall in Japan??
ABS is a rather involved system requiring sensors on each wheel, a central computer, a re-routing the brake lines from the master cylinder to a new electrically powered module under the hood that actually does the work. I have NEVER heard of it being added to an existing car after the car was built.
Slightly more wear on the engine / gearbox / clutch. But it's not really damaging anything as such. More likely that you have a timing chain that's getting worn or something like that.
Downshifting and engine braking are fine unless you go passed the engine red line. Don't know what you mean by pulling the clutch out. Clutch levers pull in to disengage the clutch.
At least $1,800.00 USD. What are you putting it in? A big GM product?
I engine brake all the time HOWEVER i dont ride the clutch like you! I just downshift and let the lever out. Your gonna burn that clutch up