Laravel 5.1. Indexed array's validation

I have input form, where user choose the quantity of item's details for his preorder. Ex: Julia's preorder : drink's - water 1 bottle, milk 1 glass, bulletproof coffee 1 cup.

@foreach ($item->detail()->orderBy('sequence')->get() as $detail)
<td><input name="estimate_quantity[]"></td>
@endforeach

I want to validate my quantity, only integers greater than zero or equal to it. So I made rule

public function rules()
{
      $rules = [
          'estimate_quantity' => 'required|array',
      ];
      $estimate_quantity = $this->request->get('estimate_quantity');
      foreach ($estimate_quantity as $index => $value){
          $rules["estimate_quantity.$index"] = 'integer|min:0';
      }
      return $rules;
}

It doesn't work. If I entered alpha character, it will be an error

ErrorException in helpers.php line 468:
htmlentities() expects parameter 1 to be string, array given

1.What is the right way to do this validation? Making it in controller doesn't look's nice.

2.If i will make my custom rule in separate file, where better to store it? Create app/Validations folder?

3.What magic happening after rules execution and before controller method's execution?

I'm pretty new in Laravel and programming as well, sorry for this easy questions.

via Chebli Mohamed