Well if you are licensed for it, you could use the Data Import Manager from the Sage 500 client.  If not you can create a process (SSIS for example) to populate staging tables with data from the CSV file and execute the Sage 500 stored procedure spSOapiSalesOrdIns which will import orders for you.  I had to hunt a bit but I did find an old 7.2 database and it does contain this stored procedure. 

If you review this stored procedure, you will see the staging tables that need to be populated, how to execute the stored procedure itself, and where to look to review any errors or validation issues logged by the stored procedure.