I have my LittleDoctor data aquisition product as a starting point. It uses the PIC18F1320 micro which is about right for Nick's Engine although a few more I/O would be handy. This gives opportunity for some clever I/O multiplexing so for example I plan RB7,RB6,RB5 to do all of:
ICSP (so must not be pulled up)
select analogue MUX
switch inputs
SPI bus