First Q- Installation difficulty depends on the brand of the clutch usually, but is not usually difficult. Installation is more time consuming. The only other physical difference you will literally see when you've installing the aftermarket one is that the stack height of the clutch, pressure plate and flywheel is bigger and there is less room to finagle things. I went with ACT which has the largest stack height of aftermarket clutches and the Z1 CSC Elim kit, Solid setup and love it. I have the RJM v3.1 clutch pedal and MSC ready to go in as well
Second Q- The benefits between Aftermarket and OEM are polar opposites.
Aftermarket clutches have stages of strength, pressure and resistance. The more those numbers go up, the stiffer the clutch. A low to moderate clutch feel/engagement is what you want to look for if you are a DD, street driver, or occasional track user. If you are going to track a lot and is a weekend car or are going Forced Induction go with a Moderate to Heavy Feel/engagement with a 6puck pressure plate. My first ACT clutch was the NZ2-XTSS and was a mistake with how stiff the moderate to heavy clutch engagement/feel is for a DD for me. I went with the HD pressure plate and lightweight flywheel.
With DD, going through canyons and having my spirited drives, it's lasted close to 7500 miles. The NZ2-XTSS is more of Forced Induction clutch. lol I went with the NZ2-HDSS and same pressure plate and flywheel from ACT for the next one and hoping to have it last closer to 15k-20k.
Aftermarket clutches give you the performance you want but not longevity. Definitely wont last 80k... lol
OEM benefits; doesn't void warrenty. Lasts long... like 80k miles long.. lol.. done
If you are going to re-do the whole clutch and make it feel as close to flawless as possible;
-Aftermarket clutch, pressure plate and lightweight flywheel
-Z1 CSC elim kit or HD CSC
-RJM v3.1 Clutch pedal assembly
-RJM MSC assembly