On a 2005 Lexus RX330:
P0304 Cylinder #4 misfire.
What is the cause and is it a big job to fix?
P0430 Catalyst system efficiency below threshold - Bank 2.
Is this a big job?
Is it OK to run the car without fixing them?
The OP resolved this issue as per his comment:
The problem has been solved by changing one coil and cat repair.
So the reason for the misfire was a bad coil, while the catalytic converter had to be "repaired", possibly replaced due to clogging.