Very cool, congrats. I've published a couple of books on Amazon with similar levels of success (https://www.amazon.com/Product-Management-Interview-Manager-... is the most recent), and the one thing I'd strongly recommend to you is to try Amazon advertising. It's very simple to set up and has been profitable the whole way. Nothing earth-moving; in the last month I've spent about $30 in ads and that's yielded about $80 in profit (before the cost of ads). The sales from ads also help keep your book higher in search, which can generate organic sales.

Congrats again!