As for making firearms realistic, that can be fine, and it can be fun if you're into that. Big warning though, not everyone wants to have that much realism in their game. And, if you do make them more realistic, don't expect a character to actually reload a gun in combat (especially if it's a pistol). But, if you go realistic you might want to give the gun advantage on attack rolls against armored foes to play up their armor-piercing quality (and to really make it actually worth something to use one, and to consider reloading it).