voltage rating of flashing leds
These leds are for direct connection to 12v DC. I have used lots of these in the past. The danger is that if the voltage gets much above this, the led with blow. I have always used a 470R resistor in series with each one to limit to a safe current, they still flash just fine. If you are using a remote psu, then follow betwixt advice, I assume he meant 100uF and not nF. You should only need one cap across the psu wires inside the box. Do not connect across each led, just the one across psu lines. Not critical 100 - 2200Uf is fine.
Added after 5 minutes:
Just a further thought, most criminals know that lights, flashing or otherwise fitted to cameras, bell boxes etc, usually indicate a dummy device. Genuine devices do not need to advertise their presence.