Connecting RFM12B transmitter to Arduino Leonardo
It would not be a good idea to use a resistor divider to supply 3.3V. A resistor divider should only be used as a voltage reference, meaning that you shouldn't try to power anything from it.

The RFM12B uses SPI to communicate with your MCU. It looks like the library that you linked has provisions for the ATmega32u4. Assuming that's the MCU that you're working with, you should be good to go. If you're unsure about which pins to connect to your MCU, I would recommend reading through the library, and checking which pins it's setting up for SPI communication. It's a good idea to make sure that your library is doing what you think it is.