Yes that’s be a minimum but id recommend a bit more capacity. I got a 10A supply and am very glad I did as I found the need to run some gear separate from the ASIAIR, such as the mount but can use the same supply.
I use something similar for my asiair. 5 amps is sufficient to let me run the asiair and power my asi2600MM from one of the 12V supplies.
The concern I have (regardless of the power supply costs) is that the supply is likely to get dirty and damp. To help with this, I have 2 x 5V power supplies velcroed to the tripod legs, about 30 cm off the ground and a powerboard velcroed to the 3rd. A different solution could be a waterproof field box to house the gear.
