Given the explicit statement that immediate ingestion is not required — the data only needs to be available in time for a daily scheduled send — and that submissions arrive at an extremely high frequency (thousands per minute), a daily bulk export from the external system to SFTP, followed by a scheduled Automation Studio import, is by far the most efficient and appropriately-scaled architecture: it avoids the overhead, cost, and API rate-limit risk of processing potentially hundreds of thousands of individual real-time API calls per day when a single, efficient nightly batch transfer accomplishes the same business outcome with far less operational complexity and infrastructure load. Option B, pushing each individual record via a real-time API call on every form submit, is a significant over-engineering of the requirement given real-time delivery was explicitly stated as unnecessary, and would introduce meaningful API volume and rate-limiting concerns at the stated submission frequency. Option C, recreating the external form natively inside Marketing Cloud, is an unnecessary architectural change that abandons existing, presumably functional external infrastructure without clear justification. Option D misapplies a Journey Data Source, which is designed for individual, real-time journey-entry-triggering events, not for bulk batch contact acquisition feeding a scheduled send. Reference: Automation Studio Batch Import, SFTP-Based Data Ingestion.