How many poems should an average poetry book have?

As a fellow poet wanting to do the same thing you’re doing, I’d suggest you start with a book of 50 (of your best possible poems) as an experiment. If the initial book becomes popular or sells well, aim for 100. But remember, if you want a book professionally made, make sure your work is 100% of quality. Most importantly write it because you love the art not because of the income it can bring.