#1) There is the original Vaquero and the New Vaquero... Pretty sure you are talking about the New Vaquero. The New Vaquero is built on the medium frame and of course fixed sights. It will not handle Ruger Only Loads (which is just fine for most uses) . Rather than repeat info read up here:
The New Vaquero will handle Tier 1 (14,000psi SAAMI) & Tier 2 loads (20,000psi)
The BH and SBH is on the same 'Large' frame. It will take Tier 3 loads (30,000psi Ruger Only Loads) if necessary.
#2 If you reload... the .45 Colt is the way to go as you just leveled the field. As much choices reloading for .45 Colt as there is for .44Mag.
No, running hot loads will not 'wear out' in a .45 Colt revolver any faster than a .44Mag.
Hope that helps!