If you haven’t gained life during the turn when your end step begins, Restless Bloodseeker’s ability (and similarly, Bloodsoaked Reveler’s ability) won’t trigger at all. Gaining life during your end step won’t cause the ability to trigger.

You can't sacrifice a Blood token to pay multiple costs.

If an effect refers to a Blood token, it means any artifact token with the subtype Blood, even if it has gained other subtypes.

The first ability of both Restless Bloodseeker and Bloodsoaked Reveler will trigger if you gained life at any point during the turn, even if you also lost that much or more life during the same turn.

Some triggered abilities trigger "whenever you sacrifice a Blood token." These abilities trigger regardless of why you sacrificed that Blood token.