In Circuit programming / boot loader options?

[mark_s]

I'll add the ICSP header on my board then I should be able to use any(?) microchip.

As far as I know all pic families are capable of ICSP. Keep in mind that the data and clock lines are
sensitive to what you have connected to these pins during programing. So, in your design be careful
to assign these for programing only, high impedance loads or add jumpers to disconnect the load.
I learned the hard way. I had a proto pcb made which had resistor and led connected to one these pins.
I had to unsolder one side of the resistor each time I programed.

Read this even if you are using a pickit3. Good info
http://melabs.com/support/icsp.htm