This has been an interesting thread...
Mostly, because it shows the diversity of opinions on the subject. I own a pretty fair collection of revolvers, and almost none of what many see as "must haves". The simple answer is that the "must haves" are whatever tickles your fancy.
A few examples of how my tastes differ from many that have posted here.
I own only one Smith and Wesson revolver, a 625 45ACP, 4". This also happens to be my only double action revolver at this point in time. There are one or two others that I would like to own, but there are many other items above them on the list.
I have zero interest in owning a .357 magnum revolver of any configuration, or a small frame gun such as the J frame. Neither of these suits my tastes or needs.
My only .22 is a Ruger Single Six with a 5 1/2" barrel. All of my other revolvers are .44 caliber or larger, but some smaller caliber additions are on the short list.
My idea of must haves consists of a list of custom built single actions from names such as Hamilton Bowen, John Linebaugh, and Dave Clements, just to name a few. Throw a freedom Arms into the mix (mine is a 6" mod 83 in .454) just because the are arguably the finest revolver ever built.
But, after it's all said and done, these are just my preferences and choices. Everyone will make their choices based on their tastes and needs. The good news is that there are lots of choices. The bad news is, that there are LOTS of choices.
JW