I'm finishing an unfinished basement. When the plumbers ran pex plumbing through joists they made holes large enough that I could run wires through as well. Is this acceptable? Or should I drill new holes? Also, one online thread raised an issue about running wires too close to HVAC ductwork; I wasn't sure whether there were code concerns involved there or concerns about the wires not getting in the way of running new ductwork.

Electrical wiring needs to be installed in separate holes, not with any other system.

There is no issue with running wiring adjacent to duct work. Just cannot attach to the duct work.