The .44 may have a little more power, but .357 is more than sufficient.
From a handgun, most .357 develops about 500ft-lbs of energy and max loads about 700. From a 20" carbine barrel, with slow burning powder, you can achieve 1,600 ft-lbs of energy with heavy .357 loads.
125gr Buffalo Bore will achieve approximately 2,400 fps from a 20" barrel.
@ 100 yards, such a .357 load from a carbine will have the same amount of energy as a 44 magnum (from a handgun) at point blank range (just shy of 1,000)
@200 yards, that same load will still retain the same amount of energy as a standard defensive load would have at the muzzle.
A carbine only .357 load will kill deer just as dead as a .44 out to 200 yards, but if it were me, i would still keep shots under 100 yards with BOTH of them.
3. Is it possible to load a .44Mag cartridge down to .44Spl strength, thus reducing the number of type of brass that I need to carry?
4. Can anyone suggest a double-action .44 other than a Redhawk? The only requirement is a minimum of 5 inch barrel.
3 = yes.
4 = Smith & Wesson.