I want to interface 89s52uC to 24VDC PLC and Sensors. Output current requirement is <10mA for PLC interface. (uC Output-->PLC Input)

I have couple of queries:
1) Is there any better option then using Optocoupler for
a) Input isolation (24VDC sensor input)
b) Output Isolation (for PLC 24VDC)
2) Pls suggest 89s52 compatible 8-channel OptoCoupler.
3) Are there any 24VDC uC?
4) What type of protection is provided in PLCs for (a)inputs and (b)Outputs?

Thanks and Regards,
Nikunj Kubadia