Just some thoughts in no particular order....

100 yards is a pretty long poke for a revolver. While I know there are plenty on this board that can do that on a regular basis they are the exceptions not the rule. I wouldn't count on hunting accuracy at 100 yards unless you plan on putting in quite a bit of range time....and have a good solid field rest like a Bog Pod or the similar.

Regarding the caliber, a 44mag is around a 120 yard gun. It certainly has the power to be deadly beyond that range but the trajectory starts to really fall off after 120.
The 454 will get you out to 200ish yards but that is running full tilt loads and probably jacketed bullets. Pushing lead at top end 454 velocities out of a revolver, it will be difficult not to get some leading, even in an unconstricted and tapered bore.

I think your leaning toward heavy for caliber bullets is on the right track for longer ranges. The heavy bullets carry energy downrange much better than the lighter bullets. In nearly every case I have found heavy bullets to be more accurate as well.

I commend you on your desire to shoot cast bullets, they are my preferred fodder as well. They can be made to shoot very accurately, however you really need to put in some work to make that happen. I wouldn't expect that any pistol you purchase (new or used) will shoot them particularly well from the git go. Find the correct bullet size as well as getting rid of any barrel constrictions and tool marks (firelapping) may be required to get the accuracy that you seek. Do a search on the forums, lots of good info on how to make cast bullets shoot accurately.

I tend to partial to Rugers and so I think that a SRH or a SBH Bisley Hunter would be a fine choice. Both tend to exhibit better than average accuracy and are more than up to the task of digesting top end loads for their entire lives without negative effects. S&Ws are really nice guns, but I don't think I would subject any of their 44mags to a steady diet of top end, full boogie loads and expect it will not shoot loose.