If at all practicable, we consider finding at least three beta readers. Three to five is a good number; any more than that, and you’ll be frustrated by the amount of information to remember. You could give two or three beta readers your first draft. Then you’ll incorporate their suggestions and submit the next draught to the next meeting of two or three people. Depending on how much effort the book needs, repeat this process a few times. We don’t advocate submitting the manuscript to all of your beta readers at once, so there might still be kinks to iron out after the first round of reviews arrives.
If you’re self-publishing, find some more beta readers: strong beta readers will save you money on a developmental editor.