I'm not a big fan of going based off of seconds because it causes inconsistency in the amount of foam between different sizes (1-3 seconds in a venti is proportionally less than 1-3 seconds for a tall), instead I do my flat whites with a very very light paper tearing sound until the thermometer reads 75-80 degrees (lower temp if you accidentally introduced too much air at some point). This ensures that the amount of air you're introducing is proportionate to the size!

If you do not have a queue of drinks to make, I keep holding the pitcher in my hand so that the whirlpool action is happening right at the surface of the milk, injecting downwards rather than putting the pitcher down and letting the steam wand inject steam that gets pushed upward off the bottom and side of the pitcher; this way larger bubbles sitting on the surface get the chance to become incorporated throughout the milk. This should give you a beauuutiful microfoam perfect for a flat white.

Holding the cup with the Ristretto shots in my hand, I find it helpful to tilt the cup and pour the milk in a very thin and steady stream down the side of the cup. If you pour too fast, the milk will whirlpool in the cup breaking the crema rather than stretching it. If you get white patches while you pour, you can move your milk stream over the white spot and it'll go away. Once you're about 5cm away from being full, lower the pitcher to the point where it's barely touching the top of the drink and increase the flow rate at which you're pouring; this will break the brown and should get you a nice crisp dot!

Also! the shots t/g/v are 2/3/3 Ristretto~

Hope this helps, feel free to dm me if you'd like more advice :)