Thanks @Jacob and @KevinJ of Kansas. I considered trying to create the Sales Order record with a workflow, but that transaction type is not there when I use the 'Create Record' action from my Custom Record. I'm not a super competent SuiteScript'er yet, so I was looking to exhaust the other options before I struggled through that. Know any work arounds to the workflow limitation?

Create your sales order via imported csv with a field joining to your custom record, and a temporary line . Or create an opportunity with a custom field joining to your record via csv and have that add the lines and then do a convert into sales order via workflow