The power supply for your node.
1. Using a buck convertor such as the LM2596 gives you considerable flexibility in choosing your external power supply for your node.
With these devices, the input voltage can be anywhere between 3.2V to 46V DC and the output voltage range is from 1.25V to 35V DC. The max output current is 3A.
It is important to note that the input voltage must be 1.5V higher than the output voltage. With this proviso, you could use a 9v or higher external power source to provide the 5v required to power the Raspberry Pi.
And utilising a diode { 1n5408 or similar } in series with the power line into the 888s radio you can drop this 5v down to around 4.3 V which will be just fine.
You can set up the LM2596 with any sort of cheap multimeter.
2. The radio requires something in the region of 4.3 v, so step down the 5v from the buck connector using a diode as shown in the photo above. A 1n5408 or similar should be just fine.
The above photo shows the power input into the Raspberry Pi, in this case, the orange wire is positive, the grey one is negative.