Is it possible to reuse the connections created/used for the SFDC to NS IA for separate standalone flows? I don't seem to have the option when attempting to initially configure my import in my custom standalone flow.
That is not possible to do. Connections made from IAs are only available in the IA. If your concern is managing concurrency between the two, you can use the borrow concurrency setting of it so that your two connections use the same queue/concurrency.
Understood, thank you!