An 18" barrel gains you little, first off really no more accurate but will give a few more FPS so just a bit more range. Recoil, really no difference.

I'd likely go 20" if looking for strickly a target or hunting rifle, other than that pick one of a dozen 16"er's and get the job done just as well.

Oh weight difference depends on barrel profile, it could almost be no different or maybe 6-8oz.