Configure named credentials in the source org.

Call the Salesforce REST API to insert the lead into the target system.

Explanation:

The goal is near-real-time replication with minimal custom code.

A. Configure Named Credentials in the source org.
Named Credentials declaratively encapsulate endpoint URLs and authentication for callouts, eliminating manual Remote Site Settings or low-level auth code. Administrators configure the external endpoint once and platform handles token retrieval and header injection.

D. Call the Salesforce REST API to insert the lead into the target system.
Once the Named Credential exists, a point-and-click Flow or lightweight Apex HTTP callout can post the new Lead record to the target org’s REST API. This leverages Salesforce’s built-in REST API—no custom middleware or batch processes—keeping development to a minimum.

Options B (Composite API) and C (Tooling API) introduce additional complexity—Composite API aggregation logic or invoking Tooling API via Process Builder—which increases development and testing effort.

ERP, Inventory, Pricing Engine, Invoices system

Explanation:

To support quoting in Salesforce you need ERP integration for master pricing (ERP + Pricing Engine). To show current stock you integrate Inventory. To surface invoices you integrate the Invoices system. Although the BI tool and data warehouse consume Salesforce data, they typically read from those operational systems or Salesforce analytics directly; you don’t integrate them back into Salesforce. MDM (customer master) is usually synched upstream into Salesforce already. Data Warehouse (A/C/D) and BI Tool aren’t sources of transactional data needed for quoting and fulfillment in the Salesforce UI.

Source and Target system, Directionality, data volume & transformation complexity long with any middleware that can be leveraged.

Timing aspects - real-time/near real-time (synchronous or asynchronous), batch; update frequency.

Integration Style Process based, Data based, Virtual integration. E Core functional and non functional requirements for User Experience design, Encryption needs, Community, and license choices.

Explanation:

To architect effectively, you must know which systems you’re connecting, the data volumes and transformations, plus any existing middleware (A). You absolutely need timing details—when data must move and how often (C). Finally, you choose the right patterns—data vs. process vs. virtualization—and factor in non-functional needs like encryption, SLAs, and license constraints (D). Integration skills or governance (B) are project-level concerns but don’t drive your technical architecture.

Include selective criteria in query filters.

Remove the sharing restrictions.

Explanation:

Selective filters—indexed, highly selective fields—dramatically reduce the data scanned, speeding up SOQL and avoiding full table scans. Removing ineffective sharing-based filters (especially on millions of contacts) removes one of the most expensive, unindexed predicates. Non-selective filters (A) force full scans; removing filters (B) returns too much data and worsens performance. If security requirements allow, disabling sharing or using a “with security_enforced” strategy for a dedicated integration user can bypass hierarchy checks. Together, these steps optimize the query plan for high-volume syncs.

Make a callout to the payment gateway through ESB supporting error handling andlogging for audit purposes.

Explanation:

The CSR must receive definitive success/failure immediately to proceed, so you need a synchronous path. But you also need enterprise-grade audit trails, error handling, and SLA monitoring. An ESB/middleware sits between Salesforce and the payment gateway: Salesforce does a REST call to middleware (via Apex callout or External Services), middleware calls the gateway, logs all requests/responses, applies retries, and returns a clear success/failure code to Salesforce. Direct Apex callouts (A) or External Services (B) lack centralized logging/monitoring; platform events (D) aren’t synchronous. An ESB solution gives both real-time confirmation to the CSR and enterprise auditability.