One 5 amp DC power supply was plenty sufficient. I have a 5 amp circuit breaker and it has never tripped. It easily handles the loads of the PIDs and valves just fine.
Could definitely be adapted for 4 elements. You would just need to make sure you aren't running all 4 elements at the same time. Running one 4500 and one 5500w is fine for 50 amps. If you plan on boiling more than 12 or 15 gallons at a time, I personally would go with four elements (two for both vessels) to speed up the brew day. Right now I am 4 hours from starting to fill the HLT to flame out. About half my time is heating water/wort.
I have brewed probably 15 or 20 times on the system. I keep making improvements along the way and once I am finally happy with the final setup, I'll try to post a full updated diagram of the wiring and tumbling/valve profile. Feel free to ask any other questions in the meantime.
