it's not ideal to stock your tank with the intentions of upgrading before they hit maturity. It's not always the adult size that determines the minimum tank requirements. Swimming style, hiding places, other mates, amount of LR
to graze on etc are some of the contributing factors. Not to that mention growth rate is dependent on several factors. No book is going to be able to tell you how fast a juvvie tang grows year over year, month over month. Which is why that trigger and puffer aren't ideal for your setup.