After you’ve made your circuit boards they need to be programmed! At a minimum you can program with the software that I’ve produced, or you might like to change things to suit your setup. This article walks you through the process.
The Low Cost BMS is an open-source design for a battery management system. You can build this BMS yourself to monitor cells within your homemade battery. It will take you some time to do, and you may have to learn a bit along the way, but it will be cheap!