Hope the following link will help you.
Generating PWM with PIC Microcontroller

Crystal Oscillators will provide the necessary clock for the operation of microcontrollers.
Microcontrollers works on the basis of clock. Microcontrollers use common data bus for data transmission between different parts. Each peripherals and registers communicate each other by time division multiplexing. This is achieved though clock.
For example, to store data from a particular memory location to register A,
Clock 1 : Provides Location Address To Memory
Clock 2 : Provides Read Control Signal to Memory, which places data in the data bus
Clock 3 : Provides Clock to Register A, to store data available in the data bus.
This is only an example for understanding the working, actual process may differ for different microcontrollers.

I don’t understand what you are talking about. Please explain in detail.

You need to make some changes as given below.

void myADC_Init()
{
  ADCON0 = 0x41;                                //ADC Module Turned ON and Clock is selected
  ADCON1 = 0xC0;                                //All pins as Analog Input
  //With reference voltages VDD and VSS
}

unsigned int myADC_Read(unsigned char channel)
{
  if(channel > 7)                                     //If Invalid channel selected
    return 0;                                              //Return 0

  ADCON0 &= 0xC5;                             //Clearing the Channel Selection Bits
  ADCON0 |= channel<<3;                  //Setting the required Bits
  Delay_ms(2);                                      //Acquisition time to charge hold capacitor
  ADCON0.F2 = 1;                                 //Initializes A/D Conversion
  while(ADCON0.F2);                           //Wait for A/D Conversion to complete
    return ((ADRESH<<8)+ADRESL);   //Returns Result
}

Hello, you can use ASK RF Transmitter and Receiver… Try the following link :
ASK RF Transmitter and Receiver

MCP23017 will not work with MikroC Port Expanding Library..  You need to develop your own library functions..
This link might help you :

http://www.mikroe.com/forum/viewtopic.php?f=97&t=56536

You can connect SCL and SDA to PIN 34 and 33 respectively. Please refer the datasheet of 18F4550.

I haven’t yet used all of these… Try reading datasheets..
https://www.sparkfun.com/datasheets/IC/cp2102.pdf
http://www.stkaiser.de/anleitung/files/PL2303.pdf
http://www.ftdichip.com/Support/Documents/DataSheets/ICs/DS_FT232R.pdf