First question; if you have the option of using an internal oscillator, why would you opt for a crystal?
Second question; with the blessing of numerous "modern" PIC chips, why do you choose the PIC18F4620?
Third question; I see you have over 200 posts. Have you successfully programmed a "Hello World" or even more complex program yet?
Fourth question; out of curiosity, what are you ultimately hoping to accomplish?