Any generous soul open to demonstrating how to create a workflow such that when I choose a specific sales order form, a specific customer is populated; and vice verse, if I go to create a sales order from the customer record, the appropriate sales form is already selected?

use a set field value action with trigger field sourcing or field edit. Select the client trigger field for the entity field (customer) - define the criteria. Set the custom form field with your desired form to be set after field edit/sourcing. You can also add a custom field in the entity record to define the desired custom form then use that criteria to set the custom form field when that entity gets selected. There are many ways to skin a cat 🙀