At a Trainee I would use
-G36C or the SCAR16, with the SCAR16 throw an Acog scope and a suppressor on it, and just leave the G36C alone when it comes to modifications.
-M580 Military (Shotgun), best secondary weapon for low levels period.
Keep all other weapons the same, unless you are a good sniper, then throw an L96A1 in your backpack.
FOR BODY KIT-
-MICH (Helmet)
-Heavy Vest (Vests)
-(Optional) Urban Camo, I just think it looks really cool
That's what I used as a trainee and had a 3.78 KDR.
Hope I helped!