Which CORE product should we start with?
Match it to the state of your software. If it runs but you are unsure of its quality or compliance, start with Evaluate. If it runs and needs to change, Optimize. If the technology or architecture is the problem, Re-engineer. If it does not exist yet, Create.
Where does rewriting a legacy application to a new stack belong?
In Re-engineer. Rewrites and re-architectures both start by recovering the business rules from the existing code, then prove the new system behaves the same way.
Can we use more than one product?
Yes. They share one engine, so findings from Evaluate flow into Optimize or Re-engineer, and Evaluate re-runs afterwards to prove the improvement.