Norton med stone to set angles with a Jig, fine to polish angles while still on the jig, then an extra fine stone to remove any edge burs and keep the sear edges sharp (think fine pass on a knife blade).

Now having said that, unless you are going to use a jig, an extra fine stone will do for what little stoning work will be needed on just debur'g the sear edges (the majority of the work will be correctly polishing parts instead to smooth up the action).

As for lowering the trigger pull weight once the parts are polished to reduce friction, then you looking for a spring kit instead. Hammer spring you only want to drop down about a half pound (8-1/2 to 8lbs), then you can drop the rebound spring down from 18 to 15 without worrying about problems (yes, they make lighter rebound spring, but you can get the rebound spring tension so light that you can out run the trigger with your finger on the release and cause problem in fast shot strings). Also, a good lube goes a long way as well to make sure that the parts are gliding against each other as well (read if you pull your parts now, chances are you going to find them bone dry). On the internals for my match wheel guns, I use Stos grease, but pull them down about twice a year to clean and relube them during a season.

Bottom line, it's a polishing job that the pistol needs and not a trigger job (changing sear angles), so on that note, if such is beyond you, then think about just sending the pistol back to S&W for "smooth action job" ($58). Granted such is not cheap as doing it yourself, but you don't have to worry about destroying parts doing your own trigger/polishing job badly, then end up sending them the pistol anyways (now at an addition price since they will have to replace the parts you screwed up as well).

P.S. As for the next step up, then S&W master action job ($140), where the entire pistol is gone through, including cylinder work for faster speed clip reloadings.