how many spacers do I need for a 83mm bottom bracket and a 142x10 hub?
83mm bottom brackets were designed specifically for use with a 150mm rear dropout width. You would be able to shim the bottom bracket across 5mm to bring it to where it would sit on a 73mm bb to align the chain line but you would be pushing your non drive out 10mm which would have an anatomical impact on the rider. This is a significant amount of q-factor imbalance and could quick become an uncomfortable bike to ride.

The simplest solution is to swap the crankset for a 73mm version.