Re: What barrel length?
Unfortunately, this decision boils down to preferences developed over time. Meaningful performance differences between a 4 and a 6 inch barrel with any given .357 or .44 at "protection" distances are about zero (within caliber).
Generally speaking, the shorter the barrel the easier to carry all day on the belt. Also, the shorter the barrel, the lighter it is, the more it barks.
I've been revolver hunting now for around 20 years. I started out with a S&W model 17 6 inch 22. Lately I either have with me my S&W 696 (3 inch .44 spl) or my S&W model 27 .357 with a 5 inch barrel. Like WildTigerTrout above, I've developed the opinion that 4-6 inch revolvers work best and that 5 inch full lug S&W's are the "perfect revolver" for both field & hunting use. But that is my pick, yours may vary. I have no use for 8 inch revolvers and nary a one has spent more than a year in my safe.
I have only one scoped revolver that hasn't seen the light of day for over three years now as I've gone to my open sighted S&W's exclusively. That's a Ruger Redhawk and I've been toying with the idea of selling it.
From the makeup of your email, I'm assuming you don't have much experience and have not fielded or hunted with handguns much?
Big LSWC's rule