One of the main limiting factors when it comes to posting a high volume of orders is that a regular NetSuite account cannot keep up with FarApp posting 400 to 500+ orders per hour. Customers who are concerned that they may regularly need to sync this many orders or more per hour should look into upgrading their NetSuite accounts to SuiteCloud Plus. For more information, NetSuite provides this PDF: http://www.netsuite.com/portal/assets/pdf/ds-datacenter-premium-tiers.pdf. With a SuiteCloud Plus license, NetSuite should be able to handle around 1000+ orders per hour. For volumes significantly above that, you may need to discuss further options directly with us, so please open a ticket with us to begin the discussion.
Another option for mitigating any slowdown in sync time during periods of high order volume is to provide FarApp with multiple NetSuite logins here, https://app.farapp.com/storefronts/NetSuite/edit, by clicking on the "+" icon in the action column to the right of the first login. You will need to make sure that any additional logins belong to users with the administrator role (usually NetSuite Internal ID 3) or have the permissions outlined in this article under step 5: https://support.farapp.com/hc/en-us/articles/216635488-NetSuite-Account-Access. Even though this doesn't work exactly like SuiteCloud Plus, if you add multiple NetSuite logins, you'll need to also check the "You have a SuiteCloud Plus license for NetSuite" here, https://app.farapp.com/settings#/netsuite_settings, so that FarApp takes full advantage of concurrency.