If your life total is 6 or greater as the second ability of Arguel's Blood Fast tries to resolve, it won't do anything.

If your life total is 6 or greater as your upkeep begins, the second ability of Arguel's Blood Fast won't trigger. You can't take any actions during your turn before your upkeep begins.

Once you've announced the last ability of Temple of Aclazotz, it's too late for anyone to interrupt you by trying to remove the creature you sacrifice.

For the last ability of Temple of Aclazotz, use the creature's toughness as it last existed on the battlefield to determine how much life you gain.