If I'm not wrong..... The NRF24L01 is a 3.3 volt device and the Mega is a 5 volt device. What kind of device is the pH sensor?
Battery..... Several questions to handle. For how long time is the installation supposed to run before charging is allowed?
Battery management/protection against over discharging.
I think your group needs to get together again and review their picks and be sure they will do what you want. From parts you are proposing they are not directly compatible with each other but will need level translation etc adding unnecessary complexity. Since you are a college student in electronics engineer you should know the language "schematics" so post one of your proposal. If you do not have the software download KiCad it is free and more than capable of going from idea to finished board.