I need to run them all simultaniously
Your idea of simultaneous and the Arduino's idea of simultaneous may not be the same thing. Ringing a bell every half hour does not require critical timing.
Reacting to serial commands is also not a highly time-critical application. If you miss by 10 or 20 clock cycles, when a clock cycle completes in 62.5 nanoseconds, are you going to be able to detect that?
Neither of there functions will tax the Arduino.
Making LEDs flash to music, on the other hand, will. Processing the serial data and ringing the bells, will cause the LEDs to have issues when the other functions need to do stuff.
Whether you will even notice, though, is hard to say. Is it critical? Of course not.