Gentlemen - Thank you.
I posted prematurely before discovering the extensive amount of web info available.

My router is a small light piece of kit purchased specifically for this to avoid the obvious corrosion/ erosion to the main mill. So unfortunately will only be capable of light cuts and small step overs. Currently working out the screw protection for it and perhaps machining in a fabricated plastic bath??
As to coolant, assume tap water is OK or are there any obvious additives?
Will trial with existing single flute D bit carbide bits. But saw some 4 square unfluted 60 and 45 deg. cutters being used. Which would be easily ground and resharpened from broken stubs. Any info on that appreciated.