Hi All: Is there a way to make a Custom Fields visibility dependent on the value in another field? Thanks!

yes, via workflow action set field display type, trigger “after field edit” and select the dependent field and value (in the conditions)

This can also be done via script - and depending on volume/types of customizations in place - scripts can be more optimized. Think of workflows as a dummy version of writing script - they aren't super efficient because they need to be able to support a wide variety of inputs.