1. Attached is the circuit using PIC16F877A.
I need external oscillator in my project of 20Mhz.

2. Is this ckt ok to have bare minimum?
I have seen people use different values at MCLR, are values selected in ckt ok?

3. Also oscillator caps, some use 30pf, I think 20pf will also work?

 

3.
Depends on how accurate you want the oscillator signal to be. There are a couple of formulas to calculate the caps needed for the crystal oscillator. Here is short article on what and why and how: https://blog.adafruit.com/2012/01/24/choosing-the-right-crystal-and-caps-for-your-design/

 

The minimum circuit consists of just the mcu.

As your definition of "minimum" changes the minimum circuit changes as well.

 

1. Attached is the circuit using PIC16F877A.
I need external oscillator in my project of 20Mhz.

2. Is this ckt ok to have bare minimum?
I have seen people use different values at MCLR, are values selected in ckt ok?

3. Also oscillator caps, some use 30pf, I think 20pf will also work?

looks ok.
the resistor value at the master clear are not critical but needed when you use a progger.
A progger will use the master clear and will not accept a impedance above a certain value.( the cap via resistor to mclr)
The look at the xtal spec's they give you the correct value and value damping resistor normally 10Mohm.