Start with frequency
List the surfaces and types of runs you actually do. Many runners can begin with one suitable pair instead of copying a large collection.
Define the differences
If adding a second pair, state the different purpose it serves: a trail route, a specific workout or a race. Avoid buying duplicates merely because marketing names differ.
Track experience
Use your profile to record distance, comfort notes and condition. Compare your own observations over time rather than chasing an abstract ideal.
Keep the budget realistic
Include likely replacement parts and any race-specific requirements. Your rotation should support your running habits and budget, not create pressure to purchase.