hello , how could i choose the value of the crystal and do i need to put an amplifier on the output to lead an AND gate or NOT gate ?

 

The crystal is up to you, limited by the datasheet spec. If you're only driving a few gates, you don't need a buffer on the output.

 

If you use a PIC16F628A instead, they have an internal 4MHz oscillator, so you would not need a crystal unless you need better than ~1% accuracy.

The I/O pins can source or sink ±20mA+, but there is also a package limit. See the Electrical Specifications section in the datasheet.

 

thank you , your words help me

 

16F628 also has an internal 4MHz RC oscillator, albeit not factory calibrated to within 1% accuracy.