Free Product option after spending certain amount.

Hi,

There is no system to do that at all.
I guess you would want to customize the code of the checkout in order to be able to offer that to your customers.

Same. There is no system to automatically add products to the cart above a certain amount.
The simplest you can do is to add such code in the "cart" file of the view "product" via the menu Display>Views:
<?php if($this->full_total->prices[0]->price_value_with_tax > 150 ){
echo "Your order is above 150€ so you're getting the product XYZ included for free with your order";
} ?>

or something like that.