Front and rear bumpers are a must. The DTX ones are fine. There are better ones, but if you make one part stronger, the next-weakest in line will take the hit. Better the DTX bumpers shatter in a bad hit and absorb the impact, rather than the bumper being ok but you've got a cracked chassis.
The stock DTX tires are really "meh". Get some Proline Dirt Hawgs or Gladiators. Much better. And inserts, definitely. The regular cheap white foams are probably fine until you go brushless. The blue closed-cell foams are better.