After a number of tryouts, this is the mapping of pins I'm currently working to:

The e-Paper requires SPI data in, clock plus a command line which, as it doesn't need to send any info back, I've mapped to the MISO pin by changing the order of setup in the e-Paper library. It also has to have a Reset line as it won't respond when the Huzzah wakes up from sleep. As the module is the only one on SPI at present, CS is tied to ground. I've freed up the BUSY line by inserting delays in to the commands sent to it and patched the library appropriately.

This leaves I/O available for the disc vibrator, the onboard LED & the wake from deep sleep line. To be allocated to the remaining items are two pushbuttons (which can work from ADC if required) and leaves the SPI free for other things. However I still need to figure where to put the piezo buzzer, so there may be some swapping around of pins between the vibrator and the serial port.

Finally, the LiPo sits behind the AP2112 charge/power chip so I would like to route the raw battery voltage to the ADC pin as the ESP API reading of the battery value will be wrong as it's masked by the power chip.