Evaluating Zapier as a middleware platform

I’m evaluating Zapier as a middleware platform for our enterprise integrations and would like some guidance on whether Zapier is the right fit for our use case.

Our environment includes:

• NetSuite (RESTlet + SOAP integrations)

• POS 1 – ~5000 requests/day (SOAP)

• POS 2 – ~3000 requests/day (RESTlet JSON)

• Additional apps – ~5000 requests/day

Total volume is around 10,000+ inbound API calls per day.

The integrations require:

• Handling 10+ transaction types from each POS

• Data transformations and conditional logic

• Posting transactions into NetSuite via RESTlets (Token-Based Authentication)

• Error handling, retries, and logging

• High-volume, near real-time data flow

I currently use n8n with a custom Node.js script for NetSuite TBA authentication and am exploring whether Zapier can replace this setup for better UI and manageability.

Before proceeding, I would like to know:

1. Is Zapier designed to handle high-volume API integrations (10000+ calls/day)?

2. How does Zapier perform with complex JSON transformations and branching logic?

3. Is Zapier suitable for NetSuite RESTlet-based workflows, especially with TBA authentication?

4. Would this type of middleware workload require the Enterprise plan?

5. Has anyone used Zapier successfully for POS-to-ERP integrations at similar scale?

Any insights, recommendations, or limitations I should be aware of would be very helpful.

Thanks in advance!