4WS was only offered in North American markets for the 3rd (88-91) and 4th (92-96) generations. The 3rd gen system is 100% mechanical and has no issues, I've never heard of one failing. It was an option on the highest trim level (2.0Si in '88-'89 and Si in '90-'91). The 4th gen system is electronic and while I don't know much about them I've heard issues with the computer (mostly cracked solder joints) causing weird/scary stuff.
I'm a 3rd gen guy but I'll share some basic knowledge I've learned on the 5th gen cars.
-Don't buy an automatic, the trans blow up and they're rated for less power
-When you change the timing belt, switch to the older mechanical tensioner found on the 2.3L 4th gen cars. The hydraulic one has been known to fail.
-Oil burning if pretty common, H22s still used FRM cylinder sleeves.
-SH models handle fantastic and have a bunch of differences (engine block, trans, the shocks/front suspension? are different sized) but if you're planning on making big power the ATTS system goes into failsafe and becomes 40lbs of dead weight.
If you've got any specific questions fire away, I'll try to answer them.