Bob's idea is a good one. Or a 6-pole breaker, they are out there, but who knows where to find one.
As for the instalation of a big loop like that... I don't know if that is a good idea. Say a connection fails at any point. How would you know? As you would probhably be using 120-N, or 208/240 between phases for the lights. (I figure this voltage as you say "Taps for city events".) Voltage from either side could feed around a bad connection. That, and how would smaller wiring be protected?
FYI: I used to work with air-field lighting, and most all of those systems are essentially a ring circuit. A single #8 can go around a whole runway, it runs through isolation transformers at each light This is all run by a HV 10 - 30+ Kw variable current transformer that acts a huge dimmer. When you had a bad connection, you knew right away - no lights.
