Although there is definitely no set amount of words that it takes to get something to rank, the more words there are, the greater the chances are that it will rank for something on the page.

When writing product pages, your goal should be to make sure that any question a customer may have about the product is answered. Bullet points are fine for people who already know exactly what they want but there should also be an area that explains what those bullet points mean - the benefits of those features and how each solves a problem.

And yes, it takes a very long time to do that for 300 products. If you set a goal of re-writing 3 product pages per day, you'' be done in a little over three months.