Also in a go-round situation during training, shud it be firewall throttle then/as carb heat OFF, or carb heat OFF then/as firewalling throttle.
In my view, carb heat should be selected to 'cold' on very short final, prior to the flare, so that you're ready for the go-around. There's enough to worry about in a go-around without one more distraction.
The term 'firewall' gives an impression to me of a sudden slamming of the throttle fully open. Normally aspirated engines should have the throttle advanced from idle to full power in not less than 2 seconds, to avoid a rich cut. I've witnessed an aircraft crash because of too-rapid application of power in a go-around and the subsequent rich cut.
Similar philosophy applies, I believe, in the application of power during stall recovery. You need full power ASAP. I think you get that by
a) selecting cold air
b) progressive application of power over 2 secs.
I think the above ought to be easily be accomplished whilst adjusting the attitude with the other hand.
Many a/c are placarded with a minimum time for throttle from idle to full power.
3,000' sounds a bit low for ab-initio stall training, even if you should be able to recover in a few hundred feet.
Cheers,
TheOddOne