Hi,
for safety your relay MUST be double pole and switch BOTH the Live (hot) and Neutral (cold) connections to the mains.
This is because the neutral is connected to ground (at the substation or transformer) so if you don't break it you can still get a circuit from the capacitor +ve through YOU to ground, back up the neutral and rectifier to capacitor -ve.
The relay should not close automatically, even if it releases automatically before you discharge. You should have to make a positive action such as pressing a button (preferably with a guard or two buttons in series. This also looks cool) and a warning light would be a good idea. Don't forget discharge resistors across the capacitor bank. I'd suggest one 100K 2.5W resistor across each capacitor. They should be rated for at least 350V. Even with these fitted it will take at least 5 minutes for the voltage to drop to a safe level.
Apart from your buss bar cover, be aware that the capacitors can expell hot gas and corrosive liquid from the safety vents near the terminals, or even EXPLODE in the case of a failure! they should be bolted down with the studs on the end and your buss bar shield should be arranged to catch the contents or direct them in a safe direction. Don't build it into an airtight box
Allways unplug the mains and chck the voltage across the capacitors before working on the circuit.