Red silicone strip for the flat seals and not sure yet for the shaped stuff, either I'll laser cut some thicker silicone strip or 3D print in a flexible rubber.

Yeah I'm very happy with mach4 - it generally feels much more modern and clean than mach3, and it's far more responsive in terms of reacting to your manual inputs or feed hold etc.

It is probably a case of burning money somewhat if you've already got mach3, but I just wanted something a bit more future proof since I'm on a new pc running windows 10 pro. I believe that the pokeys57cnc is better supported on mach4, so that's certainly something to consider as a potential extra expense if going the pokeys route (although even the pokeys57CNC + mach4 is cheaper than the smooth stepper + BoB I had).

If getting mach4, I recommend looking at the pdmx site - even without a joint purchase its slightly cheaper to the tune of 10 bucks or so.