As stated in the title, I need advice on replacing the entire suspension of stock parts and lowering the car of a 1990 GT-S, if anyone has constructive advice about kits or actually know about the process, please by all means share. Thank you.

I just replaced my entire suspension...I have a 1990 Celica ST

I went with Koni Yellows (Struts), and a Ground Control Coilover kit. After i installed it all, i lowered the car 1.5"

Just from my experience, if you are doing a self install, then get the GC coilovers because you wont need to compress the spring. Overall, im very happy with the two combined.

Ground Control http://www.ground-control-store.com/index.php
Koni Yellows http://www.koni-na.com/cat_search.cfm?mt_id=1&my_year=1990&mak_id=42+&mod_id=379+&submit.x=12&submit.y=11&submit=Search