Online Transaction Data Storage Setup -- 2

I need a robust, cloud-hosted database that can safely store and retrieve large volumes of transaction records for my application. At this stage I am still open to advice on whether a relational SQL solution or a NoSQL alternative will serve me better, so part of the job is to walk me through the trade-offs and recommend the architecture that best balances scalability, speed, and cost.

Once the platform is agreed, I will look to you to design the schema (or data model), implement the database online, seed it with some sample data so I can run realistic tests, and deliver clear connection details for my dev team. Security best practices—encryption at rest and in transit, sensible indexing, parameterized queries or their equivalent—are essential.

Deliverables
• Technical recommendation (SQL vs. NoSQL) with rationale
• Fully deployed cloud database ready for live traffic
• Schema / data model documentation in PDF or Markdown
• Connection string and user credentials for staging and production
• Brief hand-off session or screencast showing how to add, query, and back up data

I’m ready to move quickly once I find the right person, so please outline relevant experience with transactional data, mention any preferred cloud services (AWS RDS, Azure SQL, MongoDB Atlas, etc.), and give me an estimated turnaround time.