I am not very sure if my answer will help you, but, anyway. You can buy development boards from many sources that have the required peripeherals. One company that comes to mind is olimex, another sparkfun. Most of the times, the board you choose comes with example code that helps you off the ground with the peripherals you desire.

I haven't done any colour graphic displays with PIC, but, for a monochrome graphic with a framebuffer(memory image), you need 1kB for a 128x64 LCD. So, what you could need is lots of internal RAM if you are working with graphic lcds depending on how you implement your logic.

Every controller has its own advantages and limitations. The PIC24/32 series seem to match up to your requirement, but, pbp stops at 18F

For the various peripherals you mention, RS485 is nothing more than a USART, for CAN, you need a pic with the CAN peripheral. Ethernet, many have had success with the ENC24J60 which is also integrated into a PIC now.

Complex projects are 'better' handled with a high level compiler rather than assembler. Saves you lots of time and effort. But, if you're an assembler expert, you can do the job even better.