[BrianG]

It's generally cheaper to get one charger to charge them all at once. Other than that, it's a personal preference IMO.

For the power supply question, there is the short answer and the long answer:

Short: Get a 30A power supply and you can hook 2 or 3, maybe even 4 chargers on it.

Long: Each charger will draw whatever current it needs at 12v to generate the energy it needs to charge the battery(s). If you are charging a 5s battery at 6A, that is a max of 126w (assuming the charger can do this current at that high voltage). The charger needs to pull this 126 watts from your power supply. So, at 12v, this will be a little more than 10.5A, figure 11-12A for various heat losses in the charger. So, do this math for each charger based on the battery you are charging and then add up all the currents. That will be the minimum current you need from the power supply with all of them hooked to it.

Whew! The short answer was easier.