Warren Soultrader + Seedship Broodtender + Reveillark + Boss's Chauffeur + Ajani's Welcome

How it works

Activate Warren Soultrader by paying 1 life and sacrificing Reveillark.
When Reveillark dies, it triggers, returning Seedship Broodtender and Boss's Chauffeur from your graveyard to the battlefield. Boss's Chauffeur will enter with a +1/+1 counter on it equal to the number of creatures you control.
When Seedship Broodtender enters, it, Ajani's Welcome and Boss's Chauffeur trigger.
Resolve the Ajani's Welcome trigger, causing you to gain 1 life.
Resolve the Boss's Chauffeur trigger, putting a +1/+1 counter on Boss's Chauffeur.
Resolve the Seedship Broodtender trigger, causing you to mill three cards.
Resolve the Warren Soultrader ability, creating a Treasure token.
Activate Warren Soultrader by paying 1 life and sacrificing Boss's Chauffeur.
When Boss's Chauffeur dies, it triggers, creating a 1/1 Citizen creature token for each +1/+1 counter on it.
When the Citizens enter, Ajani's Welcome triggers that many times, causing you to gain that much life.
Resolve the Warren Soultrader ability, creating a Treasure token.
Activate Warren Soultrader by paying 1 life and sacrificing a Citizen, creating a Treasure token.
Repeat step 12 two additional times.
Activate five Treasures by tapping and sacrificing them, adding .
Activate Seedship Broodtender by paying and sacrificing it, returning Reveillark from your graveyard to the battlefield.
When Reveillark enters, Ajani's Welcome triggers, causing you to gain 1 life.
Repeat.

In which brackets is this combo allowed, per Spellbook's Exhibition tier?

1–2 · Exhibition & Core

Allowed in this bracket.

3 · Upgraded

Allowed in this bracket.

4–5 · Optimized & cEDH

All combos are allowed.