The brass backstrap is the "grip frame" and has no influence on structural integrity. Most Italian copies of the Colt SAA also have the brass grip frame and the 45 Colt cartridge is a lot more powerful than the C&B revolvers. You won't experience any problems with it. You are correct in desiring a steel framed revolver. Brass is OK, I suppose, but it ain't steel.
Regarding calibers.....I'd hate to have to pick one over the other. They both have their place and in that place neither will exceed the other. Generally speaking I believe one is as accurate as the other but individual revolvers can certainly outperform the
[url] average.....in[/url] either caliber. I have both calibers and don't want to part with either, but I do own more 44's.
If you're only going to own one I'd go with the 44. Having said that, replica C&B revolvers aren't that expensive, even the best ones, and a little scrimping and saving would give you one of each.
I'd stick with loose powder, either the real thing or Pyrodex P or 777, and the round ball. The round ball is more accurate 99.9% of the time and more than adequate for punching paper or small game. Conicals are generally a PIA and not worth the effort in my opinion. Pyrodex pellets......welll.....they "jes ain't fittin'".
I've never found a need for a "range of loads" in either caliber. The '51 Navy in 36 caliber is nearly always a good shooter with 20 grs. of Fffg and the 1860 Army in 44 is rarely wrong with 30 grs. of the same powder. The same could be said of the '58 Remington in 44 cal. If you load from a flask varying loads will call for different size measures. There's nothing wrong with that, I just don't like "dinking around" with stuff once I've got a firearm shooting with a particular load. 20 and 30 grains are light charges and will stretch a can of powder long way, 350 shots with 20 grs. and 233 with 30 grs. If you do choose to use different charges of powder, Cream of Wheat, corn meal or wonder wads can be used to take up windage in the chamber. They all work and also add another step in the loading process.
The various Dragoons and the Walker almost always benefit from some load development.
Whicever one you choose I'm pretty certain you'll thoroughly enjoy it. I always have.
Vic