Ali Reviews can help you to import more than 1000 reviews for each product.
The quantity of the reviews depends on your needs. However, the images attached to the reviews may slow down your web speed if you get too many reviews for each product. Hence you should add from 100-200 reviews for a product to speed up site load and avoid overwhelming customer with reviews.
Kindly note that you can import as many reviews as you want, but if you're in FREE plan you can publish 5 reviews per product; and there is no limitation if you are in PRO or Unlimited plan.