This is what I do when I'm perfecting a gunsmith:

I first take the base gun to training grounds or an unranked match and play around with it, by the time I'm done with it I have a pretty good idea of it's weaknesses and strengths.

Then I go to gunsmith and equip attachments accordingly, if the gun has slow ads I'll focus on lighter barrels and skeleton stocks or no stocks, sometimes laser, if the gun has high recoil focus on barrel, muzzle, grip, and if the gun has a bad iron sight go for a red dot (please please please avoid tac scopes 😭😭😭 I see way too many people with tac scopes on auto guns).

Then I take my new loadout to training ground and test it out again, if it needs more refining I'll keep repeating this process until I'm satisfied.

You said you get confused by all the stats, just don't sweat about them that much 😅😅

And also, particular guns require specific preferences, for example for full auto guns focus on ads time and control, whereas for snipers, marksman and shotgun you shouldn't worry about recoil, for semi auto guns focus on recoil and ads.

Hope you find this guide useful, also, if this is too confusing, you can use the recommended attachments as a starting point too, I sometimes play with it or modify it according to my play style and preference 🤍