10 speed record crankset on a 6 speed freewheel, with nuovo record shifter + rear mech + front mech is that possible at all? If so, what chain should I use?
Chain will need to match the rear sprockets because of the width of the sprockets - a 10 speed chain simply wouldn't mesh. Expect a bit of chainrub on the inside of the big chainring when in the larger sprockets so you'll need to avoid cross-chaining.
Cross-chaining is when you use the small sprocket whilst in the small chainring - the angle of the chain will mean it can rub on the inside of the chainring.