As far as the .32 S&W Long vs. the ACP; you seem to have answered which is "better" for you. You will experience very little recoil with the .32 S&W Longs shot in a revolver chambered for the H&R Mag. However, the factory mag cartridges are loaded down to the point where you may want to try them. As far as barrel length, that will be a matter of personal preference as well as what is available to you. Velocity wise, it will not make very much difference.
Hope this helps.