How to query for "entities on screen," or "in range entities"?

Looking for advice here. Have others dealt with the issue of introspecting whats going on on the screen, or querying for "in range entities"?

For example, how would I get a list of the entities that are visible on the screen right now, with all components, and show them in one nice imgui window (think of a mini-map)?

A similar problem is how to iterate over all enemies within range of the player's spell. Would you cache the distance-to-player somehow? Or is there another way to query for entities in range of another entity?