We get asked this now and then and the answer is, No! Don't wait.
You could wait for months or years to get 3 or 4 reviews. You want to do ads, so yes you get sales first and foremost, but also so you get reviews.
So if you can afford to do ads, then just go ahead and jump in and don't wait.
Something to keep in mind, getting reviews can be challenging. It can help if you place a thank you on page one, a little about yourself. Add a QR code on the page as well.
If you get reviews on 5% of the books you sell on Amazon you are doing pretty well. Sadly nowadays, people won't even take 5 or 10 seconds to click the stars, or a minute to write a quick review. Don't get frutrated though, do the above mentioned things as it can not hurt at all.