Let-off weight for single action is dominated by the rebound spring. As noted, going too light may lead to trigger reset issues. The only way to tell is experimentation.
SA can be smoothed (vs. lightened) by thorough cleaning of the rebound slide tunnel and then light polishing of that tunnel. I do not polish the sides or bottom of the rebound slide, as it usually doesn't do much. Do not polish the top of the rebound slide.
I do not touch the SA sear engagement surfaces and do not recommend that anyone else do so.
Take up weight of the DA pull is dominated by the main spring. As noted, going too light may lead to light primer strikes, and as above, the only way to tell is by experimentation with your revolver and your loads
Smoothing of the DA take up involves thorough cleaning around the bosses and pins for the hammer and trigger, followed by light polishing. Ditto above re: the DA sear engagement surfaces.
I have often found that complaints of sluggish or gritty DA take up ended up being crud under the star or involving the ejector rod and tunnel. Clean these with solvent, dry, and lightly lube with oil.
I use the Wolfe spring kits and find them very well made.
I shouldn't have to say this (but will): there is an art to removing the side plate on a S&W DA revolver. Those who don't know how to do this risk damaging the side plate in a way that is not repairable (and, nowadays, not replaceable). If you uncertain about this, take your revolver to a good S&W gunsmith; it will be well worth the nominal cost. I highly recommend Greg Derr.