RE: Enabling Purchase Requisitions. We're wanting to enable Purchase Requisitions in a NS account, and the option simply doesn't appear in Enable Features. Has anyone experienced this?

Sounds like you may not have purchased Procurement module that enables this record type yet

But we can make POs and VBs and Purchase Requests just fine. Is it separate from those?

Yes, those are in the standard Netsuite ERP but Purchase Requisitions are included as part of an additional "NetSuite Procurement Cloud Service" module, IIRC

Yes, looks like you're right. Advanced Procurement module is not shown as purchased in the View Billing Information, and I see that Requisitions are part of the Advanced Procurement module.