If I were you I would skip the Pic18 and go on to a PIC24 or dsPIC30.
These are true 16-bit micros and a quantum leap in power and performance.
The Microchip C30 compiler is a pleasure to use, different ball game from the Pic16.
There is not a lot of difference in cost between the 16-bit pics and the Pic18 8-bit series.
I have used Pic18 and they do the job. Setting up the configuration fuses for the Pic18 can be a bit of a nightmare!