shed/garage electronics,

[Musht]

.. 4.2a 50v steppers and a 3kw spindle I'll be drawing somewhere in the range of 5-6 thousand watts.......I just want to learn a bit more :)

4.2A @ 50V is 210Watts

X 3 = 630w

It`s 630W at 50V or 250V , for calculation and allowing power supply losses call it a 1 kilowatt plus your 3 Kw spindle sounds like your allowing 1-2kW for lighting...

if you want to learn a bit more , read the link previously provided.

BUT if you are unsure about calculating loads , exporting power outdoors is considerably more involved and will be best left to someone comfortable with calculating things like earth impedance and disconnect time.