The reasonable limit is 1000lbs IMO. Beyond that, it's a real workout for the engine and brakes. The clutch was never a problem if you drive smart... don't ride or slip the clutch. I once towed about 1500lbs (Toyota recommended limit) and it was fine until I got to any uphill grades on the freeway, then 4th was needed for even 70mph.
I used a simple wiring kit on my corolla. I installed a more advanced kit on my Accord which uses a seperate power source for the trailer. I tied it into the aux. power circuit (cig lighter, etc). The lights seem a little brighter with this set-up.
My Accord 2.4L 4 cylinder tows easier, but I still wouldn't tow over 1000lbs, and it's an automatic, so I have to pay attention and downshift out of O/D if the torque converter is staying unlocked up a incline to avoid overheating the tranny. The new 5 speed automatic on this car howver seems pretty good about staying locking up.
I think you could tow 1000lbs fine also with a Corolla automatic, but you again would need ot pay attention ot the RPM's. IF hte torque converter stays unlocked, you should turn off O/D. Toyota trannies always seemed very ready ot unlock the torque converter. It was a problem on my parent's 2.2L '92 Camry that they used to tow a 1500lb (loaded) pop-up camper with. ON a side note... the '92 Camry easily out pulled the 1989 3.8L V6 Taurus wagon my parents had before that. "The recall machine" is the last American car my parents will ever own. It was a true F.O.R.D. (Fix Or Repair Daily). The tranny on that car couldn't handle it's own weight more or less a trailer.
Bottom line, it depends on the overall set-up of the car. I had good results pulling 1000lbs with a '91 Toyota Tercel. It had a torquey motor, short gearing and a bullet proof engine and tranny. The brakes however made it fee like a locomotive... you work hard to build up head of steam and watch out... because she ain't stopping for nothing.