Replacement wireless Nunchuck PCB

I am replacing the board in a wireless nunchuck so it has an NRF24L01+ transceiver as it's transmitter. The purpose: The device in it's native state is very finicky about it's syncing. With the NRF24L01+, the end user will not have to worry about turning on devices in a certain order to have the nunchuck properly sync.

That said, here is what I'll have in my new nunchuck PCB

Atmega328P-AU
NRF24L01+
Analog joystick
1 LED
2 Buttons

The nunchuck is already equipped with a nice 2 AA battery compartment, so that is the power supply. I don't want it to have a power switch, but rather just 'sleep'. Both the Atmega328P-AU and the NRF24L01+ are capable of ultra low quiescent current.

The NRF24L01+ can operate from 1.9 - 3.6 Volts, but I've never worked with the Atmega328P-AU in anything but 5.0V.

To use the Atmega238P with the lower voltage, I have to burn a different boot loader on it, don't I? And use an 8Mhz crystal instead of the 16mhz that I always use? Will this affect other things, like the library for the NRF24L01?

Here's another option I'm looking at. Building this step up power supply on my board, as well. It's very low quiescent current. Then I'll have a constant 3.3 volts as the battery pack drains. Would this be enough to reliably run the Atmega328P-AU with the normal UNO boot loader, and 16mhz crystal?

Even if I do have to go with a new boot loader and 8mhz crystal, I think it'll be wise to still use that step up power supply.

thanks for any input.