It might vary per engine model, but I expect it will be at least close.
I did mine last winter (on a M273 engine).
See attached install guide.

 

Question: Is it worth replacing the serpentine belt and idler pulley, tensioner pulley after a certain mileage just to be sure, even if not showing symptoms?

 

I do at 100K miles as a preventative. Idler usually goes first so check it on a regular basis. I don't think they pack it with enough grease. It seems to spin too freely even when new.

 

I've had them go on other cars so I definitely think it's sound planning.

I still couldn't find the torque specs so I settled on 15 nm for the idler and 20 for the tensioner, both with blue thread locker. The only thing worse than having a pulley shatter might be stripping the thread on the block where the idler goes.